mysql_innodbcluster: Introduce InnoDB Cluster check

[mpeltekis]

This PR introduces a new monitoring check for MySQL InnoDB Cluster.

[zados]

• Avoid passing passwords via --password, as CLI args are visible via ps. Using a config file (like .my.cnf) would be recommended. Environment variables are an alternative but are already considered deprecated.

• L214: Returning [] on failure may mask errors and yield false OK states. Raise the exception (or wrap and re-raise with context) so the check fails loudly.

• L347: Same issue. Also clarify whether cluster_name can legitimately be unknown. Is there any use case for that?

• Use a context manager for the MySQL connection so resources are closed even on exceptions, and to set connect/read timeouts. Setting the timeouts will prevent the check from hanging.

Optional: Add type hints and brief docstrings for functions to clarify variables, types and exceptions.