Promtail: Add configuration to drop batches when rate limited by Loki

[chodges15]

What this PR does / why we need it:
This change will allow for more deterministic behavior by multitenant Promtail instances where one or more tenants are being heavily throttled due to limits exceeded within Loki. Specifically, it will reduce the performance impact of having exponential backoff cause HOL blocking for rate limit response codes while other tenants are ready to send batches.

Which issue(s) this PR fixes:
Fixes #7972

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide
• Documentation added
• Tests updated
• CHANGELOG.md updated
• Changes that require user attention or interaction to upgrade are documented in docs/sources/upgrading/_index.md

[chodges15]

I realized when looking at the metrics with this change that I was not able to distinguish between drops due to rate limiting versus other reasons like stream limiting or exhausting all retries. Use of a reason label for drops would allow alerts to differentiate.

[CLAassistant]

All committers have signed the CLA.

[grafanabot]

./tools/diff_coverage.sh ../loki-target-branch/test_results.txt test_results.txt ingester,distributor,querier,querier/queryrange,iter,storage,chunkenc,logql,loki

Change in test coverage per package. Green indicates 0 or positive change, red indicates that test coverage for a package fell.

+           ingester	0%
+        distributor	0%
+            querier	0%
+ querier/queryrange	0%
+               iter	0%
+            storage	0%
+           chunkenc	0%
+              logql	0%
+               loki	0%

[chodges15]

Enabling this option has eliminated drops we were seeing with Loki canary when using it with a shared Promtail alongside a heavily rate-limited tenant. cc @MichelHollands @chaudum @DylanGuedes for review/comment.

[MasslessParticle]

LGTM, thanks for the contribution!