server: set the keepalive MinTime for gRPC server (#38987)

[ti-chi-bot]

This is an automated cherry-pick of #38987

What problem does this PR solve?

Issue Number: close #38983

Problem Summary:

keepalive.EnforcementPolicy.MinTime is the minimum amount of time a client should wait before sending a keepalive ping. Currently, it is unset and the default value is 5 minutes, which is too long, since TopSQL gRPC client sends pings to the server every 10 seconds. As a result, "too many pings" is reported too frequently.

What is changed and how it works?

This PR changes this argument to 5 seconds.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

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]

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[ti-chi-bot]

@ti-chi-bot: This cherry pick PR is for a release branch and has not yet been approved by release team.
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/mysql-test	e4b1eb7	link	true	/test mysql-test

Full PR test history. Your PR dashboard.

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