Provide better label auto-complete in the Phlare explore view

[simonswine]

What is the improvement?:

Currently when typing a label selector in the query window, it will always use all possible series available as suggestions (which it gets by querying /series?matcher={})

As someone typing the query it would great if we could reduce the labels suggested (like the prometheus query window does).

An example:

• User starts explore and selects profile type:
  
• Now going to the label selector field we should only show the series that actually have this profile type. Can be queried using /series?matcher={__profile_type__="process_cpu:cpu:nanoseconds:cpu:nanoseconds"}
• Now the user types {namespace="prod", pod=, rather than show all pod name values, we should fire another request and gather values that already match namespace="prod" either by reusing the previous result or firing a new request to the series endpoint.

Is there anything else we need to know?:

This is how it works in Loki/Prometheus explore already (I think)

[aocenas]

@simonswine is this existing API?

[simonswine]

@simonswine is this existing API?

Yes should be there since the start

[aocenas]

@simonswine when changing the backend to support both pyroscope and phlare I changed this so we use LabelNames and LabelValues API, so we don't get all the possible series at once (which at some occasions was >30mb response) but for each label on demand. This means we cannot use the /series api with the matcher but would be nice if the LabelNames and LabelValues have such param which they don't it seems.