[VOL-5315] Add support for tool pre-commit and repo:onf-make

.pre-commit-config.yaml
-----------------------
  o Install basic config for pre-commit tool use.

lf/transition.mk
----------------
  o Legacy mode: add deps to checkout submodule
    when repo:onf-make library makefiles are included.

lf/onf-make/makefiles/commands/pre-commit/
------------------------------------------
  o Define convenience target 'pre-commit
  o A virtualenv is installed on demand as a dependency.
  o Invoke tool pre-commit.

lf/
Makefile
.gitmodules
-----------
  o Add repo:onf-make as a git submodule.
  o Facilitate replacing local copy & paste makefiles/ with
    a refactored library equivalent.

Change-Id: Ife154010c6ff3c8f1df38c8ebbef0d3b178cb529
diff --git a/lf/include.mk b/lf/include.mk
new file mode 100644
index 0000000..5d52907
--- /dev/null
+++ b/lf/include.mk
@@ -0,0 +1,109 @@
+# -*- makefile -*-
+# -----------------------------------------------------------------------
+# Copyright 2023-2024 Open Networking Foundation Contributors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# -----------------------------------------------------------------------
+# SPDX-FileCopyrightText: 2023-2024 Open Networking Foundation Contributors
+# SPDX-License-Identifier: Apache-2.0
+# -----------------------------------------------------------------------
+
+$(if $(DEBUG),$(warning ENTER))
+
+## -----------------------------------------------------------------------
+## Infer path to cloned sandbox root
+## [TODO] Deprecate TOP=
+## -----------------------------------------------------------------------
+lf-sbx-root   := $(abspath $(lastword $(MAKEFILE_LIST)))
+lf-sbx-root   := $(subst /lf/include.mk,$(null),$(lf-sbx-root))
+
+## -----------------------------------------------------------------------
+## Define vars based on relative import (normalize symlinks)
+## Usage: include makefiles/onf/include.mk
+## -----------------------------------------------------------------------
+onf-mk-abs    := $(abspath $(lastword $(MAKEFILE_LIST)))
+onf-mk-top    := $(subst /include.mk,$(null),$(onf-mk-abs))
+onf-mk-lib    := $(onf-mk-top)/onf-make/makefiles
+onf-mk-loc    := $(onf-mk-top)/local
+
+TOP           ?= $(patsubst %/makefiles/include.mk,%,$(onf-mk-abs))
+
+## -----------------------------------------------------------------------
+## This variable is a bridge to help transition away from legacy makefiles.
+## -----------------------------------------------------------------------
+legacy-mk     := $(lf-sbx-root)/makefiles
+
+## ------------------------------------------------------
+## Two distinct vars needed to access library or project
+## ------------------------------------------------------
+ONF_MAKEDIR ?= $(onf-mk-lib)
+MAKEDIR     ?= $(onf-mk-loc)
+
+# -----------------------------------------------------------------------
+# Load per-repository conditionals
+# Load late else alter MAKEFILE_LIST
+# NOTE: config.mk can be removed if dynamic feature detection by
+#       file extension is added.
+# -----------------------------------------------------------------------
+include $(wildcard $(lf-sbx-root)/config.mk $(lf-sbx-root)/lf/config.mk)
+
+## -----------------------------------------------------------------------
+## Load makefiles in order:
+##   1) Library constants and logic loaded first
+##   2) Parameterize and augment targets from local (repo specific)
+## -----------------------------------------------------------------------
+include $(onf-mk-lib)/include.mk
+include $(onf-mk-loc)/include.mk
+
+## Define late so caller (?- env --ignore-environment -?)
+GIT ?= /usr/bin/env git
+
+## -----------------------------------------------------------------------
+## Intent: This target will update dependent git-submodule to the latest
+##         version available from the remote repository.  Subsequently
+##         a checkin will be needed to make the submodule update permanent.
+## -----------------------------------------------------------------------
+.PHONY: update-git-submodules
+update-git-submodules:
+	$(GIT) submodule foreach git pull
+
+## -----------------------------------------------------------------------
+## Intent: On-demand cloning of git submodule(s).
+## -----------------------------------------------------------------------
+## Trigger: include $(onf-mk-lib)/include.mk
+##   - When the make command attempts to include a makefile from the
+##     repo:onf-make submodule, this target/dependency will initialize
+##     and checkout all submodules the current repository depends on.
+## -----------------------------------------------------------------------
+.PHONY: git-submodules
+git-submodules : $(onf-mk-lib)/include.mk
+
+$(onf-mk-lib)/include.mk:
+
+	$(call banner-enter,(Checkout git submodules))
+
+	$(GIT) submodule update --init --recursive
+
+	$(call banner-leave,(Checkout git submodules))
+
+## -----------------------------------------------------------------------
+## -----------------------------------------------------------------------
+help-git :
+	@printf '  %-33.33s %s\n' 'git-submodules' \
+	  'Init and recursive checkout of git submodule(s)'
+	@printf '  %-33.33s %s\n' 'update-git-submodules' \
+	  'Update git submodule(s) to the latest version'
+
+$(if $(DEBUG),$(warning LEAVE))
+
+# [EOF]