Adds a new function to the `//sa` to ensure that a MariaDB config passed
in via SA `setDefault` or via DSN perform the following validations:
1. Correct quoting for strings and string enums to prevent future
problems such as PR #6683 from occurring.
2. Each system variable we care to use is scoped as SESSION, rather than
strictly GLOBAL.
3. Detect system variables passed in that are not in a curated list of
variables we care about.
4. Validate that values for booleans, floats, integers, and strings at
least pass basic a regex.
This change is in a bit of a weird place. The ideal place for this
change would be `go-sql-driver/mysql`, but since that driver handles the
general case of MySQL-compatible connections to the database, we're
implementing this validation in Boulder instead. We're confident about
the specific versions of MariaDB running in staging/prod and that the
database vendor won't change underneath us, which is why I decided to
take this approach. However, this change will bind us tighter to MariaDB
than MySQL due to the specific variables we're checking. An up-to-date
list of MariaDB system variables can be found
[here.](https://mariadb.com/kb/en/server-system-variables/)
Fixes https://github.com/letsencrypt/boulder/issues/6687.
Phil Porada