Timestamps are logged automatically by GitHub Actions and can be
made visible using log settings easily. Hence we remove the
unnecessary timestamps here to make the logs look much cleaner.
We have disabled CircleCI and are using GitHub Actions for automated
testing.
docs: Changed context from CircleCI to Github Actions and wrote
some documentation specific to GH Actions.
tools: Replaced env checks for CIRCLECI with GITHUB_ACTION.
README: Use GitHub Actions build status badge.
Sphinx/ReadTheDocs supports automatically translating links written as
to `.md` files to point to the corresponding `.html` files, so this
migration does not change the resulting HTML output in ReadTheDocs.
But it does fix apparent broken links on GitHub.
This doesn't prevent people from reading the documentation on GitHub
(so doesn't mitigate the fact that some rtd-specific syntax does not
render properly on GH), but it will prevent us from getting erroneous
issues reported about the hyperlinks not working.
Fixes: #11087.