[2.x] chore(core): add MariaDB to frontend DatabaseDriver enum

[DavideIadeluca]

Fixes #0000
With MariaDB and MySQL diverging more and more we've noticed and changed in the Framework that both databases need to be treaded separatly. Some more information on this can be viewed athttps://github.com//pull/4682

Changes proposed in this pull request:
Add MariaDB to the DatabaseDriver enum

Reviewers should focus on:

Screenshot

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).
• Core developer confirmed locally this works as intended.
• Tests have been added, or are not appropriate here.

Required changes:

• Related documentation PR: (Remove if irrelevant)