[Cache] Document Redis auth option and DSN username/auth parameters

[ckrack]

This PR documents the previously undocumented auth connection option for the Redis cache adapter and improves the DSN authentication examples.

Changes:

• Mention username support in the DSN description text
• Update DSN example to use a custom username instead of default
• Add example for auth[] query parameter syntax
• Document the auth option in the options array and the "Available Options" section
• Add note that Predis ignores the auth option (credentials must be provided via DSN)

Context:

This was requested in the discussion on symfony/symfony#63324, where it was pointed out that the auth parameter was undocumented.

[nicolas-grekas]

Cool thanks.
Ppl are also looking for differentiating sentinel vs master auth, see symfony/symfony#62218
Let's hint about this use case!

[ckrack]

no, a/an is chosen by the sound of the following word. y-sounds like username, university etc use the consonant version. So the "a" should be correct.

[MrYamous]

My bad

[nicolas-grekas]

Let's account for symfony/symfony#63391 here also, and likely update the messenger doc too. 🙏

[ckrack]

Let's account for symfony/symfony#63391 here also, and likely update the messenger doc too. 🙏

Should i target 7.4 then?

[nicolas-grekas]

Ah right, yes, 7.4 is good enough

[ckrack]

@nicolas-grekas rebased onto 7.4 and added examples and notes to both component docs.

Sorry for the codeowner ping @xabbuh, that's due to a rebase on 7.4