[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/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..758cef6
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "lf/onf-make"]
+	path = lf/onf-make
+	url = https://github.com/opencord/onf-make.git