Better support for high cardinality labels values retrieval

[simonswine]

Is your feature request related to a problem? Please describe.

When a profile series, currently contains a high cardinality label, the API experience is fairly poor:

We will just return the full list of values lexicographically sorted.

Describe the solution you'd like

I would like to limit the values returned on high cardinality label values and instead dynamically switch to auto suggestions.

A rough implementation plan could be like this:

• [ ] Limit maximum amount of label values we return, and introduce an API change to allow for a field that will show that the list has been truncated
• [ ] Support request parameter for supplying a prefix (??) for auto suggest
• [ ] Introduce metadata caching on the backend side in order to reduce work required, keep latency low