Upgrade parts of the documentation to 2.0 style

Upgrade parts of the documentation to 2.0 style

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I've started to work on #7659, implementing the low hanging fruit changes for now. Some still remain, which I've outlined as a [comment](https://github.com/sqlalchemy/sqlalchemy/issues/7659#issuecomment-1073029151), and probably also some that I didn't catch.

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This pull request is:

- [x] A documentation / typographical error fix
	- Good to go, no issue or tests are needed
- [ ] A short code fix
	- please include the issue number, and create an issue if none exists, which
	  must include a complete example of the issue.  one line code fixes without an
	  issue and demonstration will not be accepted.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.   one line code fixes without tests will not be accepted.
- [ ] A new feature implementation
	- please include the issue number, and create an issue if none exists, which must
	  include a complete example of how the feature would look.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.

**Have a nice day!**

Closes: #7829
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/7829
Pull-request-sha: a89561dd0c96c2f9a6d992fa0fb94683afaf7e30

Change-Id: Ibc5ea94b5c4b2d7b1cf7bea24f4394d1fde749be