Alloy-Mixin: allow config overwrite

[gaantunes]

PR Description

Implementing the following changes:

• Allow overwriting the config values for dashboards, instead of always pulling it from the local config file.
• grafanaDashboards and prometheusAlerts hidden, according to the mixin schema.
• allow filter selector for metrics to avoid Grafana Agent metrics query collision, and setting default to job="integrations/self"
• allow filter selector for logs to avoid pulling logs from other platforms, and setting default to service_name="alloy"
• fixing bugs reported by @rfratto in the comment below

Which issue(s) this PR fixes

Notes to the Reviewer

PR Checklist

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

[rfratto]

@gaantunes While we're working through fixes for #808, I found a few other issues that PR introduced:

• Some panels are broken:
  • The "Nodes" and "Node table" panels in "Alloy / Cluster Overview" aren't using string substitution properly and so %(groupSelector)s is appearing literally in the panel query.
  • The "Component evaluation histogram" panel in "Alloy / Controller" has a stray ' at the end of the query breaking it
• The "Alloy logs overview" dashboard is missing the alloy-mixin tag present on all other dashboards.
• The "Alloy logs overview" dashboard doesn't align with the naming conventions of the other dashboards; Alloy / Logs Overview would be more in-line with the other dashboard names.

You can reproduce this locally if you navigate to the example directory and run

docker compose --profile=alloy up -d

then navigate to http://localhost:3000 for the Grafana instance it spawns. The Docker Compose environment also watches for changes to the mixin so you can test changes live.

After you're done, you can tear it down with

docker compose --profile=alloy down

[gaantunes]

@rfratto should be ready for a re-review.

[rfratto]

(sorry, I had reviewed this last week but never submitted my review 😞)

[rfratto]

Thanks, this is coming along well!

[rfratto]

I skimmed through the diffs in our internal deployment of the mixin, looks good. Thanks!