feat(core): Add ignored client report event drop reason

[Lms24]

This PR adds ignored as a new allowed client report discard reason. The new reason can already be used (see ticket for details). Technically, we only need it right now for span-first to record ignoreSpans hits. But this reason also meant for more telemetry types, so we can merge it into develop already.

see: https://develop.sentry.dev/sdk/telemetry/client-reports/#envelope-item-payload

closes https://linear.app/getsentry/issue/FE-678/add-new-ignore-discard-reason-for-client-reports

[linear]

FE-678 Add new `ignore` discard reason for client reports

[github-actions]

node-overhead report 🧳

Note: This is a synthetic benchmark with a minimal express app and does not necessarily reflect the real-world performance impact in an application.
⚠️ Warning: Base artifact is not the latest one, because the latest workflow run is not done yet. This may lead to incorrect results. Try to re-run all tests to get up to date results.

Scenario	Requests/s	% of Baseline	Prev. Requests/s	Change %
GET Baseline	9,240	-	8,746	+6%
GET With Sentry	1,704	18%	1,615	+6%
GET With Sentry (error only)	5,904	64%	5,930	-0%
POST Baseline	1,188	-	1,097	+8%
POST With Sentry	590	50%	527	+12%
POST With Sentry (error only)	1,063	89%	964	+10%
MYSQL Baseline	3,282	-	3,256	+1%
MYSQL With Sentry	486	15%	427	+14%
MYSQL With Sentry (error only)	2,677	82%	2,610	+3%

View base workflow run