Alloy-Mixin: add severity and description to alerts, plus other improvements

[gaantunes]

PR Description

This is adapting Alloy Mixin alerts to comply with https://monitoring.mixins.dev/ best practices.

• Adding summary and description annotations, removing message
• Adding severity (warning for all alerts - lmk if you want another severity for any of these)
• Adding labels to descriptions to help troubleshooting alert
• Adding instance label into queries for controller and otel alerts - this is instance granular is it not?

Additionally:

• Making job template non-multi variable, to avoid picking up unwanted metrics
• Changing Running Instances count panel within controller dashboard to group by instance, since this is duplicating the values

Which issue(s) this PR fixes

Notes to the Reviewer

During integration testing, we noticed alloy_component_controller_evaluating emits 2 active series for each instance, thus duplicating the running instances panel value.

PR Checklist

• [ ] CHANGELOG.md updated
• [ ] Documentation added
• [ ] Tests updated
• [ ] Config converters updated

[gaantunes]

@mattdurham have updated it to exclude the instance label, if guess we can merge now?