fix: group together 4xx and 5xx HTTP responses for prometheus [DET-8336]

[azhou-determined]

Description

HTTP responses outside of /det and /api/v1 are not grouped, meaning 4xx/5xx responses will each create a new Prometheus metric label group and increase cardinality exponentially.

Solution is to group and obscure all requests outside of /det and /api/v1 returning error codes.

Test Plan

• hit many nonexisting urls in Determined, and check /debug/prom/metrics. The urls should be grouped under "/**"

Commentary (optional)

Checklist

• [ ] Changes have been manually QA'd
• [ ] User-facing API changes need the "User-facing API Change" label.
• [ ] Release notes should be added as a separate file under docs/release-notes/. See Release Note for details.
• [ ] Licenses should be included for new code which was copied and/or modified from any external code.
• [ ] If modifying /webui/react/src/shared/ verify make -C webui/react test-shared passes.

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