Do not log config when the config is not changed

[djshow832]

What problem does this PR solve?

Issue Number: close #680

Problem Summary:
When the operator sets the label periodically, TiProxy keeps reporting the same config. Logs are too many.

What is changed and how it works:

• Keep a byte format of the current config in the memory
• Compare the latest config bytes with the original one, only log it, calculate checksum, and notify listeners when the config has changed

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.

- Do not log config when the config is not changed

[ti-chi-bot]

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 78.57143% with 3 lines in your changes missing coverage. Please review.

Please upload report for BASE (main@26c66bc). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
pkg/manager/config/config.go	75.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #694   +/-   ##
=======================================
  Coverage        ?   70.02%           
=======================================
  Files           ?      105           
  Lines           ?    10017           
  Branches        ?        0           
=======================================
  Hits            ?     7014           
  Misses          ?     2511           
  Partials        ?      492           

Flag	Coverage Δ
unit	70.02% <78.57%> (?)

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