[WIP] Support remote write v2

[SungJin1212]

This PR adds remote write 2.0 ingestion.
It is in WIP and the implementation is based on remote write 2.0 docs.(https://prometheus.io/docs/specs/remote_write_spec_2_0)

Which issue(s) this PR fixes:
Fixes #6116

What I did and what will do (this PR covers)

• add remote write v2 proto
• ingest sample, (native) histogram, metadata, and exemplar
• add response headers to distributor/Ingester response

X-Prometheus-Remote-Write-Samples-Written <count of all successfully written Samples>
X-Prometheus-Remote-Write-Histograms-Written <count of all successfully written Histogram samples>
X-Prometheus-Remote-Write-Exemplars-Written <count of all successfully written Exemplars>

• add remote write v2 Distributor/Ingester test (porting existing Distributor/Ingester tests to v2)
• Implement HA tracker
• Implement relabel
• add prealloc timeseries like v1

Future works (other PRs cover)

• [] performance test between v1 and v2

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[stale]

This issue has been automatically marked as stale because it has not had any activity in the past 60 days. It will be closed in 15 days if no further activity occurs. Thank you for your contributions.