Fix Grafana dashboard for AsyncAPIs

[jackmpcollins]

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Changes

• Fix typo: async_queue_length -> async_queued so that the list of api_names is populated (currently empty)
• Use =~ with api_name where missing to enable displaying multiple AsyncAPIs on a panel
• For the "In-Flight Requests" panel include the api_name in the legend

Testing

I have made the corresponding updates manually through the Grafana UI for our deployed Cortex cluster. AsyncAPIs now list in the "Cortex / AsyncAPI" dashboard and the dashboard works when multiple AsyncAPIs are selected.

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checklist:

• [ ] run make test and make lint
• [ ] test manually (i.e. build/push all images, restart operator, and re-deploy APIs)
• [ ] update examples
• [ ] update docs and add any new files to summary.md (view in gitbook after merging)
• [ ] cherry-pick into release branches if applicable
• [ ] alert the dev team if the dev environment changed