tso: pre-initialize the TSO metrics with the group label

[JmPotato]

What problem does this PR solve?

Issue Number: ref #7011.

What is changed and how does it work?

Pre-initialize the TSO metrics with the group label.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• lhy1024
• nolouch

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[codecov]

Codecov Report

Merging #7012 (b256008) into master (7a4e1e2) will decrease coverage by 0.03%.
The diff coverage is 85.84%.

@@            Coverage Diff             @@
##           master    #7012      +/-   ##
==========================================
- Coverage   74.20%   74.17%   -0.03%     
==========================================
  Files         433      433              
  Lines       46101    46139      +38     
==========================================
+ Hits        34209    34225      +16     
- Misses       8872     8892      +20     
- Partials     3020     3022       +2     

Flag	Coverage Δ
unittests	74.17% <85.84%> (-0.03%)	⬇️

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[JmPotato]

/merge

[ti-chi-bot]

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 1d46992