[VOL-5051] - Triage bbsim build

[VOL-5092] - verify_bbsim_unit-test repository failures in jenkins job history.

makefiles/*
-----------
  o Merge in latest library makefiles.
  o Some legacy retained:
      tools.mk => makefiles/docker/include.mk
      makefiles/lint/docker/*.mk (replace with docker/include.mk.new)

Makefile
--------
  o Remove bogus foobar target.
  o Target docs-lint now maps to library target lint-doc8.

docs/Makefile
-------------
  o venv install now handled by makefiles/virtualenv.mk
  o Replaced inlined doc8 lint target with makefiles/lint/doc8 (lint-doc8)
  o Use std defines for SHELL= and other constants.
  o Replace separator ';' with '&&' in commands using venv (detect errors).

config.mk
---------
  o Enable lint targets for doc8, docker & json.
  o More lint checks can be enabled but cleanup is needed first.

docs/Makefile
requirements.txt
----------------
  o Identified a few python module problems documented in VOL-5092.
  o Makefile wild target(%) matching stray dependencies so hardcode sphinx targets to act on.
  o Added hyphen/success to "make docs" until VOL-5092 can be straightened out.

Change-Id: Ibe4006747ee610bfe8ac0fdbb339e5e18e6e9176
diff --git a/makefiles/help/variables.mk b/makefiles/help/variables.mk
new file mode 100644
index 0000000..a22b179
--- /dev/null
+++ b/makefiles/help/variables.mk
@@ -0,0 +1,36 @@
+# -*- makefile -*-
+# -----------------------------------------------------------------------
+# Copyright 2017-2023 Open Networking Foundation
+#
+# 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.
+# -----------------------------------------------------------------------
+
+# Include variables.mk after library makefiles have been included
+
+ifdef VERBOSE
+  help :: help-variables
+else
+  help ::
+	@echo
+	@echo '[VARIABLES] - Conditional makefile behavior'
+	@echo '  see also: help-variables'
+endif
+
+help-variables:
+	@echo
+	@echo '[VARIABLES] - Conditional makefile behavior'
+	@echo '  NO_PATCHES=           Do not apply patches to the python virtualenv'
+	@echo '  NO_OTHER_REPO_DOCS=   No foreign repos, only apply target to local sources.'
+	@echo '  VERBOSE=              Display extended help topics'
+
+# [EOF]