log: print welcom after config init

[xhebox]

What problem does this PR solve?

Issue Number: close #453

Problem Summary: The root cause that tiup-cluster did not print the welcome log is that, tiproxy prints the message to stdout, which goes to system units.

And it is basically impossible/very hard to redirect that to the log file on tiup-cluster. Instead, we just print the log after config initialization,

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

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None

[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:

• 2024-01-18 06:20:19.185226235 +0000 UTC m=+423260.749523937: ☑️ agreed by djshow832.