fix(taskworker): Add associated brokers to task execution metric

[enochtangg]

When task execution gets slow, we see certain task brokers backlog, not all brokers. This PR adds a a tag onto the task execution latency metric to identify if certain workers associated to a broker is being slow somehow.

[sentry-io]

🔍 Existing Issues For Review

Your pull request is modifying functions with the following pre-existing issues:

📄 File: src/sentry/taskworker/workerchild.py

Function	Unhandled Issue
handle_alarm	ProcessingDeadlineExceeded: execution deadline of 90 seconds exceeded by sentry.tasks.drain_outbox_shards ... Event Count: 1

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