workflows: automatically label ecosystems issues and PRs

[katiehockman]

What does this PR do?

Adds a workflow to detect "contrib" in the title of an issue or a PR, and automatically add the apm:ecosystem label if present.

Motivation

We've been doing this manually for some time, and it'd be nice to have this happen automatically.

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.

For Datadog employees:

• If this PR touches code that handles credentials of any kind, such as Datadog API keys, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

Unsure? Have a question? Request a review!

[pr-commenter]

Benchmarks

Benchmark execution time: 2023-10-11 13:29:45

Comparing candidate commit 96e6570 in PR branch katie.hockman/label-ecosystems with baseline commit ef73efb in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 40 metrics, 1 unstable metrics.

[felixge]

LGTM (haven't tested, but skimmed the diff)