api: add grpc and diagnostics

[xhebox]

Issue Number: ref #387

Problem Summary: GRPC service is implemented by github.com/pingcap/sysutil. So this PR is trvial. Main changes are in pkg/server/api/http.go.

Check List

Tests

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

Notable changes

• Has configuration change
• Has HTTP API interfaces change
• Has tiproxyctl change
• Other user behavior changes

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

Support diagnosticspb grpc service for cluster_xxx system tables

[xhebox]

/retest

[djshow832]

Can you add some tests? The test coverage of this pkg is still 0.

[djshow832]

Fix CI

[xhebox]

Fix CI

Done

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: djshow832

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-11-02 06:10:46.335283245 +0000 UTC m=+3106243.922393391: ☑️ agreed by djshow832.