[Metricbeat] Missing documentation in SQL module

[sorantis]

The SQL module documentation doesn't explain well how to work with the module. E.g. there is no indication which SQL drivers are supported, how each driver can be configured, limitations (if any) on what types of queries can be executed, etc.
Update the module documentation with relevant description and examples of configuration for the supported drivers.

Part of #15048

[elasticmachine]

Pinging @elastic/integrations-services (Team:Services)

[sayden]

Original community PR: #13257

[jsoriano]

Added reference to this issue in the meta ticket for this module #15048

[botelastic]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[sorantis]

keep open

[botelastic]

Hi!
We just realized that we haven't looked into this issue in a while. We're sorry!

We're labeling this issue as Stale to make it hit our filters and make sure we get back to it as soon as possible. In the meantime, it'd be extremely helpful if you could take a look at it as well and confirm its relevance. A simple comment with a nice emoji will be enough :+1.
Thank you for your contribution!

[botelastic]

Hi!
We just realized that we haven't looked into this issue in a while. We're sorry!

We're labeling this issue as Stale to make it hit our filters and make sure we get back to it as soon as possible. In the meantime, it'd be extremely helpful if you could take a look at it as well and confirm its relevance. A simple comment with a nice emoji will be enough :+1.
Thank you for your contribution!