metrics: add keyspace label to show tso request details

[bufferflies]

What problem does this PR solve?

Issue Number: Close #9780, ref #9707

What is changed and how does it work?

Check List

Tests

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

Code changes

• Has the configuration change
• Has HTTP API interfaces changed (Don't forget to add the declarative for the new API)
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• PR to update pingcap/tiup:
• Need to cherry-pick to the release branch

Release note

None.

[ti-chi-bot[bot]]

Skipping CI for Draft Pull Request. If you want CI signal for your change, please convert it to an actual PR. You can still manually trigger a test run with /test all

[ti-chi-bot[bot]]

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[codecov[bot]]

Codecov Report

:x: Patch coverage is 93.87755% with 3 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 76.80%. Comparing base (e2f7162) to head (bdd8eed). :warning: Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9778      +/-   ##
==========================================
- Coverage   76.88%   76.80%   -0.08%     
==========================================
  Files         485      486       +1     
  Lines       77372    77586     +214     
==========================================
+ Hits        59485    59592     +107     
- Misses      14270    14346      +76     
- Partials     3617     3648      +31     

Flag	Coverage Δ
unittests	76.80% <93.87%> (-0.08%)	:arrow_down:

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[ti-chi-bot[bot]]

@bufferflies: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
non-block/pull-unit-test-next-gen	b28df15f2a15c701423e5c69b317de276bdb34ee	link	false	/test pull-unit-test-next-gen
pull-unit-test-next-gen-1	b28df15f2a15c701423e5c69b317de276bdb34ee	link	true	/test pull-unit-test-next-gen-1
pull-unit-test-next-gen-2	b28df15f2a15c701423e5c69b317de276bdb34ee	link	true	/test pull-unit-test-next-gen-2
pull-unit-test-next-gen-3	b28df15f2a15c701423e5c69b317de276bdb34ee	link	true	/test pull-unit-test-next-gen-3

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