Updated documentation for June 2021 provider release

[potiuk]

---

^ Add meaningful description above

Read the Pull Request Guidelines for more information.
In case of fundamental code change, Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in UPDATING.md.

[potiuk]

Those are the docs for the June >=2.1. Providers. Changelogs are now semi-automatically generated (including first attempt to automatically classify the changes to features/bug fixes (very simple for now and always requiring manual review and moving changes around). I've done it this way that we keep the "irrelevant" changes as comments so they are not present in the generated documentation. Please take a look - I'd love to merge it asap so that I can release all the packages after "auto-apply defaults" change.

[potiuk]

One day if/when we go to semantic commits (maybe) - we will be able to fully automate changelog generation this way for all providers.

[github-actions]

The PR most likely needs to run full matrix of tests because it modifies parts of the core of Airflow. However, committers might decide to merge it quickly and take the risk. If they don't merge it quickly - please rebase it to the latest main at your convenience, or amend the last commit of the PR, and push it with --force-with-lease.