metrics: distinguish events of server level and connection level

[jackysp]

What problem does this PR solve?

Issue Number: close #48289

Problem Summary:

What is changed and how it works?

Rename it.

Check List

Tests

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

1. start a cluster
2. reload the tidb.json
3. set max_execution_time to a lower values, then make it take effect
4. check on grafana
   

• No need to test

  • I checked and no code files have been changed.

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

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[codecov]

Codecov Report

Merging #48290 (6bd19a2) into master (4f00ece) will increase coverage by 1.3105%.
Report is 2 commits behind head on master.
The diff coverage is 100.0000%.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #48290        +/-   ##
================================================
+ Coverage   71.4917%   72.8022%   +1.3105%     
================================================
  Files          1402       1425        +23     
  Lines        406373     412762      +6389     
================================================
+ Hits         290523     300500      +9977     
+ Misses        96016      93345      -2671     
+ Partials      19834      18917       -917     

Flag	Coverage Δ
integration	43.1640% <100.0000%> (?)
unit	71.4279% <100.0000%> (-0.0638%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	53.9874% <ø> (ø)
parser	∅ <ø> (∅)
br	48.6730% <ø> (-4.2626%)	⬇️

[zimulala]

LGTM

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, zimulala

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Needs approval from an approver in each of these files:

• OWNERS [hawkingrei,zimulala]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-11-05 13:10:31.704603641 +0000 UTC m=+3390629.291713787: ☑️ agreed by hawkingrei.
• 2023-11-06 02:37:37.731808932 +0000 UTC m=+3439055.318919077: ☑️ agreed by zimulala.

[hawkingrei]

/ok-to-test