ci: run current OATS consumer suites

[zeitlinger]

Summary

• replace the legacy direct OATS invocation with a root oats.toml plus the current CLI
• keep the existing example-exporter suites but run them through shared LGTM fixtures and a gcx wrapper
• preserve the custom-check path while moving the suite onto the current OATS runtime

Why

This gives the current OATS implementation real downstream CI coverage for:

• compose-backed metric suites
• custom-check execution
• HTTP/protobuf and gRPC exporter variants
• current gcx-driven query flow

Validation

• /tmp/oats --config oats.toml --list
• CI will run mise run acceptance-test on this branch using the current OATS CLI

[zeitlinger]

I pushed follow-up fixes for the current-OATS CI bootstrap and then an empty commit to retrigger Actions (1b25fb8). The PR head has updated, but I am still not seeing any new workflow runs for the new head SHA yet. Could a maintainer check whether Actions need approval/retriggering for this fork PR so we can get real consumer CI validation?

[zeitlinger]

Temporarily closing to retrigger PR workflows on the latest consumer-validation head; reopening immediately.

[zeitlinger]

I reproduced the merge conflict locally and rebased the branch onto current main, but publishing the rewritten branch is blocked by GitHub workflow-file permissions: rebasing onto current main pulls in upstream .github/workflows/* commits, and PAT-based force-push is rejected without workflow scope. If a maintainer can use GitHub's Update branch button or rebase this draft branch from a workflow-write-capable checkout, the current-OATS consumer changes themselves are already resolved locally.