Expose cardinality of labels as metrics

[Amoolaa]

Is your feature request related to a problem? Please describe.
In our multi-tenanted setup, we frequently have teams using high cardinality loki labels and not following labelling best practices.

Describe the solution you'd like
While this output is exposed in logcli via something like logcli series '{}' --since=1h --analyze-labels, my proposal is to expose this data under a metrics endpoint.

It allows:

• Users to quickly view this data in a dashboard and adjust their labelling practices
• A historic view on cardinality counts
• Alerting on high cardinality counts, for either us (the platform team) or the users

I think giving some sort of out-of-the-box functionality (vs getting users to logcli their way to view this data) will be beneficial to users and platforms teams for monitoring usage.

Describe alternatives you've considered
Writing our own service that calls the logcli endpoint, parses the output and exposes as metrics. This isn't hard to do, but if there's an opportunity to contribute to the upstream project for others, why not?

Even just giving an option to expose the output of the --analyze-labels as json would be better, for parsing reasons

[mveitas]

100% agree with this and in support of exposing this information