chore(logs): modifying the capitalization consistency of the logs

[pangruoran]

What this PR does / why we need it:

Which issue this PR fixes:
part of #3708

Special notes for your reviewer:

It has been split from PR #4992 to make it easier to review.
PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• the CHANGELOG.md release notes have been updated to reflect any significant (and particularly user-facing) changes introduced by this PR

[codecov]

Codecov Report

Attention: 12 lines in your changes are missing coverage. Please review.

Comparison is base (62e6df8) 75.5% compared to head (5adc181) 75.5%.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #5033   +/-   ##
=====================================
  Coverage   75.5%   75.5%           
=====================================
  Files        167     167           
  Lines      18881   18881           
=====================================
+ Hits       14262   14268    +6     
+ Misses      3791    3788    -3     
+ Partials     828     825    -3     

Files	Coverage Δ
internal/adminapi/backoff_strategy_konnect.go	100.0% <100.0%> (ø)
internal/clients/readiness.go	89.1% <100.0%> (ø)
...ntrollers/configuration/kongadminapi_controller.go	61.4% <100.0%> (ø)
...nal/controllers/gateway/gatewayclass_controller.go	79.2% <100.0%> (ø)
internal/dataplane/sendconfig/sendconfig.go	82.4% <83.3%> (ø)
internal/manager/run.go	54.9% <83.3%> (ø)
internal/controllers/gateway/gateway_controller.go	72.7% <66.6%> (-0.2%)	⬇️

... and 3 files with indirect coverage changes

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[randmonkey]

According to recommendation, error messages should not be capitalized. I did not comment on every place, but all messages in fmt.Errorf() and errors.New() should not be capitalized.

[randmonkey]

I searched for log messages (by finding Info(...) and Error(...) calls) and found some log messages are not updated.

Already updated