conf.py: add a bitbake_git extlink

To make references to the bitbake repo, add an extlink for it and use it
in the docs with ":bitbake_git:`lib/bb/utils.py </tree/lib/bb/utils.py>`".

Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>
(From yocto-docs rev: 5efb5f678278276aebd6809ab785dcea8c732de3)

Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
(cherry picked from commit 8bf3c656ec54a582c75ca7c135121a15f8e4f631)
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

documentation/conf.py

@@ -90,6 +90,7 @@ rst_prolog = """
 
 # external links and substitutions
 extlinks = {
+    'bitbake_git': ('https://git.openembedded.org/bitbake%s', None),
     'cve_mitre': ('https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-%s', 'CVE-%s'),
     'cve_nist': ('https://nvd.nist.gov/vuln/detail/CVE-%s', 'CVE-%s'),
     'yocto_home': ('https://www.yoctoproject.org%s', None),