feat(dashboard): backpressure: remove the support for Promethues data source

[fuyufjh]

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What's changed and what's your intention?

Our dashboard allows getting back-pressure data from both Prometheus and Meta node directly. However, this makes the frontend code more and more messy and hard to maintain.

This PR removes the support for Prometheus. In next PR you will see the code can be simplified a lot.

Checklist

• I have written necessary rustdoc comments.
• I have added necessary unit tests and integration tests.
• I have added test labels as necessary.
• I have added fuzzing tests or opened an issue to track them.
• My PR contains breaking changes.
• My PR changes performance-critical code, so I will run (micro) benchmarks and present the results.
• My PR contains critical fixes that are necessary to be merged into the latest release.

Documentation

• My PR needs documentation updates.

Release note

[fuyufjh]

• feat(dashboard): add throughput (rows/s) metrics #19972
• refactor(dashboard): refactor back-pressure calculation #19954
• feat(dashboard): backpressure: remove the support for Promethues data source #19953 👈 (View in Graphite)
• main

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[yufansong]

LGTM