Docs: Hint about potential high cardinality metrics

[m1keil]

What this PR does / why we need it:
Add warning about potential high cardinality metrics due to the file path being included in some of the metrics.
Depending on the setup, such config can result in a very large amount of label values, which is not recommended by Prometheus.
This can result in increased storage, slow down of queries, extra costs and so on.

Address what has been discussed in #5553.

Which issue(s) this PR fixes:
Fixes #5553

Checklist

• Documentation added
• Tests updated
• Add an entry in the CHANGELOG.md about the changes.

[CLAassistant]

All committers have signed the CLA.

[dannykopping]

Thanks for submitting this @m1keil 👍
I'll leave this for @KMiller-Grafana to review

[kavirajk]

LGTM 👍

[dannykopping]

We should mention Promtail here explicitly... "per tracked file" only makes sense in the context of Promtail.

Removed redundancy:

Suggested change

	Some of the Loki observability metrics are emitted per tracked file (active), with the file path included in labels.
	Some of the Loki metrics are emitted per tracked file (active), with the file path included in labels.

A hint about which metrics are emitted per tracked file would be kind to the operator, so they are able to configure the scraping to avoid this issue.

[stale]

Hi! This issue has been automatically marked as stale because it has not had any
activity in the past 30 days.

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[KMiller-Grafana]

Not stale. . .

[dannykopping]

@KMiller-Grafana can you please re-review? Your requested changes are blocking a merge

[KMiller-Grafana]

Thanks for the changes. Sorry for the delay in my re-review.