Update Oracle dialect doc, mostly to prefer python-oracledb

Update Oracle dialect doc, mostly to prefer python-oracledb

### Description

Small updates for Oracle Database dialect documentation.

- prefer python-oracledb over cx_Oracle
- Prefer the product name 'Oracle Database' over the company name 'Oracle'
- update links
- modernize

This is a refresh of existing content.

I decided the apparently now duplicated sections between cx_Oracle and python-oracledb were justified for clarity due to the inevitable differences.

This pull request is:

- [x] A documentation / typographical / small typing error fix
	- Good to go, no issue or tests are needed

**Have a nice day!**

Closes: #12078
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/12078
Pull-request-sha: 7c4dcf94032af295a6836e9412a4367b716f2de5

Change-Id: I3678976f5524ee164dc31b3122b224ae37060b71