proxy: add new dimension to exclude cplane latency

[khanova]

Problem

Currently cplane communication is a part of the latency monitoring. It doesn't allow to setup the proper alerting based on proxy latency.

Summary of changes

Added dimension to exclude cplane latency.

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

2490 tests run: 2367 passed, 0 failed, 123 skipped (full report)

---

Code coverage* (full report)

• functions: 28.8% (6982 of 24253 functions)
• lines: 47.4% (42897 of 90559 lines)

* collected from Rust tests only

---

_{The comment gets automatically updated with the latest test results
9c5493b at 2024-03-06T10:48:52.156Z :recycle:}

[khanova]

Check with preview, seems to work.