[TECH DEBT] Deprecate MySQL Modules

Description of the tech debt to be addressed, include links and screenshots

Deprecating all MySQL functionality in Salt and moving it to:
https://github.com/saltstack/saltext-mysql

First Salt version with Vault no longer present in the core: 3009.0

To be removed:

tests/pytests/functional/cache/test_mysql.py
tests/pytests/functional/modules/test_mysql.py
tests/pytests/functional/states/test_mysql.py
tests/pytests/unit/cache/test_mysql_cache.py
tests/pytests/unit/modules/test_mysql.py
tests/pytests/unit/returners/test_mysql.py
tests/pytests/unit/pillar/test_mysql.py
tests/pytests/unit/states/mysql
tests/integration/modules/test_mysql.py
tests/integration/files/mysql_returner_archiver_data.sql
tests/integration/files/file/base/mysql_utf8.sls
tests/integration/files/file/base/mysql
tests/integration/states/test_mysql_database.py
tests/integration/states/test_mysql_grants.py
tests/support/pytest/mysql.py
salt/cache/mysql_cache.py
salt/modules/mysql.py
salt/returners/mysql.py
salt/pillar/mysql.py
salt/auth/mysql.py
salt/states/mysql_grants.py
salt/states/mysql_user.py
salt/states/mysql_database.py
salt/states/mysql_query.py
doc/ref/cache/all/salt.cache.mysql_cache.rst
doc/ref/modules/all/salt.modules.mysql.rst
doc/ref/returners/all/salt.returners.mysql.rst
doc/ref/pillar/all/salt.pillar.mysql.rst
doc/ref/auth/all/salt.auth.mysql.rst
doc/ref/states/all/salt.states.mysql_query.rst
doc/ref/states/all/salt.states.mysql_grants.rst
doc/ref/states/all/salt.states.mysql_database.rst
doc/ref/states/all/salt.states.mysql_user.rst

Review the removal list in the issue, including the MySQL modules, cache, returner, pillar, auth, states, tests, fixtures, and documentation. Start by checking references to these paths and the saltext-mysql project to understand the migration boundary. Done means the listed Salt functionality and associated tests and docs are removed without leaving broken references.