Add opt in feature telemetry

[mattdurham]

Add telemetry on major feature flags being used, this will help Agent team determine if a feature is getting enough traction to graduate from experimental/beta and what users are finding helpful/useful.

Ideals:

• Opt in only, likely via a flag
• No identifiable information, ie no ips, usernames, ect
• No sensitive information was sent, ie record that remote configuration is being used but not the URL
• Configurable endpoint and easily view what is sent (add to logs?)

The initial dataset is the feature flags used, and if the scraping service is being used.

[rfratto]

Agree that this would be useful for us to find out who is using what so we can make more informed development decisions, and 100% agree that it's very important for this to be opt-in. (Though I'm personally OK with it being set in the YAML so you can opt-out dynamically without having to restart)

Loki recently added usage reports in to its server too: grafana/loki#5361
Current Loki code is here: https://github.com/grafana/loki/tree/main/pkg/usagestats

[rfratto]

I asked around how this works for Loki and Grafana and was told that:

• Grafana sends the usage report every 24 hours when enabled, and Loki sends it every 4 hours when enabled. The frequency is flexible but too frequent can make it harder to do aggregations.
• Both Loki and Grafana store a random UUID fingerprint for each instance so that usage stats from the same process can be correlated but still be anonymous and non-identifiable

[github-actions]

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Thank you for your contributions!

[marctc]

Ideals:

* Opt in only, likely via a flag

We decided to change it to opt out. The reason is temporarly documented here.