Reduce the amount of Gantry templating

[bridgetbarnes]

There's a lot of templating in the Gantry files that could be repeated via skuba templating instead of Gantry templating, as it ideally wouldn't change much once the files exist.

I'm raising this as a draft to check everyone's fine with these fields being changed

[changeset-bot]

⚠️ No Changeset found

Latest commit: 1516db1

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[zbrydon]

We're happy removing this?

[72636c]

Sorry for 🐌, but I think this aligns with the long-term view of recommending OTel over Datadog-specific application-level tooling. However, we'll need to rip out seek-datadog-custom-metrics from the templates to properly decouple from the Datadog agent sidecar.

Are you interested in picking this up in this PR @bridgetbarnes, or should we split out?