proxy, util: recover from connection panic

[djshow832]

What problem does this PR solve?

Issue Number: close #363

Problem Summary:
Previously, if a connection panics, the server quits. The server should still run.

What is changed and how it works:
Call recover() in defer in each connection to prevent the panic from passing to the server.
As for the common modules, such as the cert manager, router, logger manager, panic is critical, so it's better to let the server quit if they encounter errors.

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.

None

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: xhebox

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-09-13 14:10:22.564048812 +0000 UTC m=+94588.531636858: ☑️ agreed by xhebox.