[chore][mysqlreceiver] Add stability level per metric (open-telemetry#42973)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description

open-telemetry/opentelemetry-collector#13756
added support for exposing metrics' stability level in the generated
documentation. This PR makes use of this functionality.

We start by setting the stability of all metrics to `development`. More
info about levels can be found at
https://github.com/open-telemetry/opentelemetry-specification/blob/v1.49.0/oteps/0232-maturity-of-otel.md#maturity-levels.

Related to:
- open-telemetry/opentelemetry-collector#11878
- open-telemetry/opentelemetry-collector#13297
-
open-telemetry#35325
-
open-telemetry#42809

<!-- Issue number (e.g. open-telemetry#1234) or full URL to issue, if applicable. -->
#### Link to tracking issue
Fixes ~

<!--Describe what testing was performed and which tests were added.-->
#### Testing
~

<!--Describe the documentation added.-->
#### Documentation
Updated

<!--Please delete paragraphs that you did not use before submitting.-->

Signed-off-by: ChrsMark <[email protected]>

Author: ChrsMark