Add metric of waiting for tSafe latency

[bigsheeper]

/kind improvement

[mergify[bot]]

@bigsheeper E2e jenkins job failed, comment /run-cpu-e2e can trigger the job again.

[codecov[bot]]

Codecov Report

Merging #24765 (f78d18e) into master (b77bee6) will decrease coverage by 0.02%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #24765      +/-   ##
==========================================
- Coverage   82.61%   82.60%   -0.02%     
==========================================
  Files         776      776              
  Lines      101894   101905      +11     
==========================================
- Hits        84182    84174       -8     
- Misses      14693    14705      +12     
- Partials     3019     3026       +7     

Impacted Files	Coverage Δ
internal/querynodev2/delegator/delegator.go	87.77% <100.00%> (+0.34%)	:arrow_up:
pkg/metrics/querynode_metrics.go	100.00% <100.00%> (ø)

... and 18 files with indirect coverage changes

[bigsheeper]

/run-cpu-e2e

[czs007]

/approve /lgtm

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bigsheeper, czs007

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