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.

To merge this cherry pick:

1. It must be approved by the approvers firstly.
2. AFTER it has been approved by approvers, please wait for the cherry-pick merging approval from triage owners.

Details

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[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-7.1@bc598fa). Click here to learn what that means.
The diff coverage is n/a.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.1     #50556   +/-   ##
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  Coverage               ?   73.4139%           
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  Hits                   ?     278020           
  Misses                 ?      82929           
  Partials               ?      17753           

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei

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Details

Needs approval from an approver in each of these files:

• OWNERS [hawkingrei]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-01-22 08:18:43.319794047 +0000 UTC m=+775964.884091750: ☑️ agreed by hawkingrei.