[otel-agent] Add MySQL preset

[matej-g]

Description

Resolves ES-29.

This change adds and documents how to use the MySQL presets from the upstream chart with otel-agent.

• Adds values for both standard collector and CRD
• Disabled by default
• Documented usage, required parameters etc.

How Has This Been Tested?

Locally on a test cluster

Checklist:

• I have updated the relevant Helm chart(s) version(s)
• I have updated the relevant component changelog(s)
• This change does not affect any particular component (e.g. it's CI or docs change)

[matej-g]

Strictly speaking we could go with this version, which is currently the latest in the fork, but we'd be missing some metrics and improvements. I'd prefer to wait for coralogix/opentelemetry-helm-charts#16 to be resolved and bump afterwards.

[matej-g]

Closing this in favor of #255, since the changes should go to infrastructure collector and not agent.