metrics: Add err label for TiFlashQueryTotalCounter (#25317)

[ti-srebot]

cherry-pick #25317 to release-4.0
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/25326

After apply modifications, you can push your change to this PR via:

git push [email protected]:ti-srebot/tidb.git pr/25326:release-4.0-d37062fe5135

---

What problem does this PR solve?

Pre Pull Request: #23426

What is changed and how it works?

What's Changed:
Add error label for TiFlashQueryTotalCounter
How it Works:
Add error label for TiFlashQueryTotalCounter, so that we can observe the error type in prometheus, and ignore some error we don't want to observe.

Related changes

• Need to cherry-pick to the release branch

Check List

Tests

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

Side effects

• Performance regression
  • Consumes more MEM

Release note

• metrics: Add err label for TiFlashQueryTotalCounter

[ti-chi-bot]

@ti-srebot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick, it must first be approved by the collaborators.

AFTER it has been approved by collaborators, please ping the release team in a comment to request a cherry pick review.

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[ti-srebot]

/run-all-tests

[ti-srebot]

@jyz0309 you're already a collaborator in bot's repo.

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• xhebox

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