Add August 2021 Provider's documentation

[potiuk]

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Read the Pull Request Guidelines for more information.
In case of fundamental code change, Airflow Improvement Proposal (AIP) is needed.
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In case of backwards incompatible changes please leave a note in UPDATING.md.

[potiuk]

This time we will release almost all the providers (but vast majority of them just contains the new "connection-type" in provider-info that will allow to optimise importing of connections in Airflow 2.2 - it's fully backwards compatible with 2.1 and it's tested automatically for connection discovery so it's safe to release it now.

[github-actions]

The PR is likely OK to be merged with just subset of tests for default Python and Database versions without running the full matrix of tests, because it does not modify the core of Airflow. If the committers decide that the full tests matrix is needed, they will add the label 'full tests needed'. Then you should rebase to the latest main or amend the last commit of the PR, and push it with --force-with-lease.

[potiuk]

I will update and merge it after #17900 -> I want to use the opportunity that we release nearly all providers due to "2.2.0" upcoming optimisation to fix all deprecation warnings in examples and code of the providers!