fix(prometheus_exporter sink): fix race condition in prometheus export sink for incremental metrics

[akashvbabu91]

Summary

Move the incremental aggregation logic into the write lock scope in run(), making the read-modify-write operation atomic. This fixes the issue in

Vector configuration

How did you test this PR?

• Smoke tested in our org stacks to verify counters don't decrement except for when they are reset by flush_period_secs
• Tested on both amd and arm machines

Change Type

• Bug fix
• New feature
• Dependencies
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

References

• Closes: Prometheus exporter sink: Race condition in incremental metric aggregation #24830

Notes

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