client: return total wait duration in resource interceptor OnRequestWait call (#7488)

[ti-chi-bot]

This is an automated cherry-pick of #7488

What problem does this PR solve?

Issue Number: ref #5851

What is changed and how does it work?

return total wait duration in resource interceptor OnRequestWait call so we can track the wait duration in tidb slow log.

Check List

Tests

• Unit test

Code changes

Side effects

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[bot]]

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[ti-chi-bot[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.

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[ti-chi-bot[bot]]

PR needs rebase.

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[rleungx]

Confirmed with @glorv, release-7.1 doesn't need this cp.