Docs: Add docs new version files created by `make docs` to .gitignore

Files are:

 - docs/AWS_S3_BUCKET
 - docs/GIT_BRANCH
 - docs/VERSION

Docker-DCO-1.1-Signed-off-by: O.S. Tezer <ostezer@gmail.com> (github: ostezer)

Update:

 - Remove unnecessary last blankline
Merge pull request #5371 from ostezer/docs-add-docs-versioning-files-to-gitignore

Docs: Add docs new version files created by `make docs` to .gitignore