documentation: conf.py: add knob for loading appropriate objects.inv

Yocto Project releases use a specific Bitbake release. Currently the
bitbake: mapping is pointing to the current master version of Bitbake
documentation. This is an issue if some links disappear over time and
someone is still building old documentation (which is the case on the YP
autobuilder for example). Also, the documentation at the current master
version of Bitbake might not be correct for the Yocto Project version
associated with the doc the user is currently looking at, potentially
causing confusion.

In master branch, nothing needs to be done. For release branches, the
bitbake_version variable needs to be set accordingly. See
https://wiki.yoctoproject.org/wiki/Releases for the mapping.

Cc: Quentin Schulz <foss+yocto@0leil.net>
(From yocto-docs rev: 457a591a46c57519046f9e3f8bffd632bb2275ea)

Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Reviewed-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/conf.py

@@ -17,6 +17,7 @@ import sys
 import datetime
 
 current_version = "dev"
+bitbake_version = "" # Leave empty for development branch
 
 # String used in sidebar
 version = 'Version: ' + current_version
@@ -90,7 +91,7 @@ extlinks = {
 
 # Intersphinx config to use cross reference with Bitbake user manual
 intersphinx_mapping = {
-    'bitbake': ('https://docs.yoctoproject.org/bitbake/', None)
+    'bitbake': ('https://docs.yoctoproject.org/bitbake/' + bitbake_version, None)
 }
 
 # Suppress "WARNING: unknown mimetype for ..."