feat(spans): Also write inp metrics to transactions name space

[edwardgou-sentry]

Right now INP metrics are span metric distributions with percentiles. We rely on these percentiles in the product UI.

There are plans to disable storing percentiles for distributions under the spans namespace, so we must move INP metrics to the transactions namespace as a workaround to keep INP percentiles. The plan is to extract these transaction namespace INP metrics for 90 days until we have enough data to switch over and deprecate the spans namespace INP metrics.

[jjbayer]

This is already extracted as d:transactions/measurements.score.total@ratio (PR):

relay/relay-dynamic-config/src/defaults.rs

Lines 815 to 816 in 5dff966

	mri: "d:transactions/measurements.score.total@ratio".into(),
	field: Some("span.measurements.score.total.value".into()),

@edwardgou-sentry can we get rid of d:transactions/measurements.score.total@ratio in favor of the new d:transactions/webvital.score.total@ratio? Or is the one with measurements. still used by the product? Asking because the measurements. one has caused problems before.

Either way we should keep only one of the two metrics.

[edwardgou-sentry]

Yeah I think you're right, we probably don't need two of these

[iambriccardo]

Changes LGTM, will leave it to @phacops for the final approval.

[edwardgou-sentry]

I've heard that the team is now planning to make an exception to keep percentiles for the inp metric (d:spans/webvital.inp@millisecond). So we actually do not need this change anymore 😅

Closing this pr for now, but we can reopen and discuss if it becomes needed again