refine resource group task_count metric

[guo-shaoge]

What problem does this PR solve?

Issue Number: close #9595

Problem Summary: make task count metric to type Counter to avoid we cannot observe very fast MPP Task execution.

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

None

[yibin87]

LGTM

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gengliqi, yibin87

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• OWNERS [gengliqi,yibin87]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-11-08 09:58:30.560983853 +0000 UTC m=+4672.751852845: ☑️ agreed by gengliqi.
• 2024-11-08 09:59:06.838065289 +0000 UTC m=+4709.028934280: ☑️ agreed by yibin87.

[guo-shaoge]

/cherry-pick release-8.5

[ti-chi-bot]

@guo-shaoge: new pull request created to branch release-8.5: #9768.

In response to this:

/cherry-pick release-8.5

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[ti-chi-bot]

In response to a cherrypick label: new pull request could not be created: failed to create pull request against pingcap/tiflash#release-8.5 from head ti-chi-bot:cherry-pick-9594-to-release-8.5: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"A pull request already exists for ti-chi-bot:cherry-pick-9594-to-release-8.5."}],"documentation_url":"https://docs.github.com/rest/pulls/pulls#create-a-pull-request","status":"422"}