Adding typing to Postgres dialect file.

Adding typing to Postgres dialect file.

Adding typing information for various parameters for Postgres types (in accordance to the docs).

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: #9594
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/9594
Pull-request-sha: c7e39a219108f9e81ad22c008a664b62f09f9d5f

Change-Id: I91b377c246c728885a99df297de7a8933835c540