Prepare RC1 docs for June 2023 wave of Providers

[eladkal]

---

^ Add meaningful description above

Read the Pull Request Guidelines for more information.
In case of fundamental code changes, an 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 a newsfragment file, named {pr_number}.significant.rst or {issue_number}.significant.rst, in newsfragments.

[eladkal]

============================== apache-airflow-providers-smtp ==============================
------------------------------ Error   1 --------------------
/opt/airflow/docs/apache-airflow-providers-smtp/notifications/smtp_notifier_howto_guide.rst: WARNING: document isn't included in any toctree

will be addressed in #32006

[potiuk]

Two NITs

[eladkal]

Hopefully should be good to go now