client: fix pd client panic

[zeminzhou]

What problem does this PR solve?

Issue Number: Close #6440

What is changed and how does it work?

Initialize metrics, but do not register

Check List

Tests

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

1. change tidb code: call WithInitMetrics(false) when creating pd client.
2. start tidb cluster
3. curl http://127.0.0.1:10080/metrics
   

Code changes

• Has the configuration change
• Has HTTP API interfaces changed (Don't forget to add the declarative for the new API)
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• PR to update pingcap/tiup:
• Need to cherry-pick to the release branch

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• binshi-bing
• rleungx

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[binshi-bing]

LGTM

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.08 🎉

Comparison is base (b159dd2) 74.97% compared to head (dc6b5f8) 75.05%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6441      +/-   ##
==========================================
+ Coverage   74.97%   75.05%   +0.08%     
==========================================
  Files         409      409              
  Lines       41491    41493       +2     
==========================================
+ Hits        31107    31144      +37     
+ Misses       7676     7647      -29     
+ Partials     2708     2702       -6     

Flag	Coverage Δ
unittests	75.05% <100.00%> (+0.08%)	⬆️

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

Impacted Files	Coverage Δ
client/metrics.go	100.00% <100.00%> (ø)

... and 36 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.

[rleungx]

Do we still need to call it inside initAndRegisterMetrics?

[zeminzhou]

yesh, if callers want to add const labels, we should reinitialize variables with const labels.

[rleungx]

/run-check-issue-triage-complete

[rleungx]

/merge

[ti-chi-bot]

@rleungx: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[ti-chi-bot]

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

Commit hash: dc6b5f8