Fix the fixed clientid in quic demo client & Add configuration for quic.

[wanghaEMQ]

• Fix the fixed clientid in quic demo client.
• Add some comments to configuration for quic.

[codecov-commenter]

Codecov Report

Patch coverage has no change and project coverage change: -0.05 ⚠️

Comparison is base (0a0d8e7) 61.45% compared to head (461da10) 61.41%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #156      +/-   ##
==========================================
- Coverage   61.45%   61.41%   -0.05%     
==========================================
  Files          99       99              
  Lines       26485    26484       -1     
==========================================
- Hits        16276    16264      -12     
- Misses      10209    10220      +11     

Impacted Files	Coverage Δ
src/mqtt/protocol/mqtt/mqtt_quic.c	0.00% <ø> (ø)

... and 17 files with indirect coverage changes

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