conn, util: make opentracing work again (#50551)

[ti-chi-bot]

This is an automated cherry-pick of #50551

What problem does this PR solve?

Issue Number: close #50508

Problem Summary: Caused by #40825, miss root span for opentracing tools.

What changed and how does it work?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
  Start a TiDB cluster as opentracing.enable not work after v7.1.0 #50508 said, and use JaegerUI to get trace info success.
  
• 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

[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by triage owners.
Adding the do-not-merge/cherry-pick-not-approved label.

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[ti-chi-bot]

@ti-chi-bot: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/check_dev_2	0f03b66	link	true	/test check-dev2

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[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-7.5@3f84f3f). Click here to learn what that means.
The diff coverage is n/a.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.5     #50557   +/-   ##
================================================
  Coverage               ?   71.9704%           
================================================
  Files                  ?       1400           
  Lines                  ?     406617           
  Branches               ?          0           
================================================
  Hits                   ?     292644           
  Misses                 ?      94282           
  Partials               ?      19691           

Flag	Coverage Δ
unit	71.9704% <0.0000%> (?)

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

Components	Coverage Δ
dumpling	53.9913% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	53.2715% <0.0000%> (?)

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-01-21 06:56:13.06310141 +0000 UTC m=+684614.627399099: ☑️ agreed by hawkingrei.