[PR #7761/33180344 backport][stable-8] Add github_app_access_token lookup plugin (#7802)

Add github_app_access_token lookup plugin (#7761)

* Add github_app_access_token lookup plugin

* Fix a typo in short_description

* Remove unused MockOpenUrl

* Fix MockJWT to be used on jwt_instance instead

* Fix a bunch of pep8 and pylint issue

* Remove JWT from requirements, also default jwt_instance and jwk_from_pem so they can be mocked

* Update version added

Co-authored-by: Felix Fontein <felix@fontein.de>

* Update git reference in doc

Co-authored-by: Felix Fontein <felix@fontein.de>

* Update plugins/lookup/github_app_access_token.py

Co-authored-by: Felix Fontein <felix@fontein.de>

* Expose token expiry as a configurable option

* Update BOTMETA.yml

* Update documentation

* Update example with var, so it is more readable

Co-authored-by: Felix Fontein <felix@fontein.de>

* Apply suggestions from code review

Co-authored-by: Felix Fontein <felix@fontein.de>

---------

Co-authored-by: Felix Fontein <felix@fontein.de>
(cherry picked from commit 3318034403)

Co-authored-by: weisheng-p <weisheng-p@users.noreply.github.com>

.github/BOTMETA.yml

@@ -241,6 +241,8 @@ files:
   $lookups/filetree.py:
     maintainers: dagwieers
   $lookups/flattened.py: {}
+  $lookups/github_app_access_token.py:
+    maintainers: weisheng-p
   $lookups/hiera.py:
     maintainers: jparrill
   $lookups/keyring.py: {}