fix: parse ttl to int in key auth credentials

[randmonkey]

What this PR does / why we need it:

parse ttl field of kong key-auth credentials to int type to fix error of invalid type when filling the ttl in secret to Kong credential.

Which issue this PR fixes:

fixes #2734
Special notes for your reviewer:

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

Base: 74.1% // Head: 74.0% // Decreases project coverage by -0.0% ⚠️

Coverage data is based on head (45a1e67) compared to base (996bc14).
Patch coverage: 62.5% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #3319     +/-   ##
=======================================
- Coverage   74.1%   74.0%   -0.1%     
=======================================
  Files        110     110             
  Lines      13255   13263      +8     
=======================================
- Hits        9826    9822      -4     
- Misses      2802    2809      +7     
- Partials     627     632      +5     

Impacted Files	Coverage Δ
internal/dataplane/kongstate/kongstate.go	69.1% <62.5%> (-0.3%)	⬇️
...nternal/controllers/gateway/udproute_controller.go	73.6% <0.0%> (-2.8%)	⬇️
...nternal/controllers/gateway/tlsroute_controller.go	73.2% <0.0%> (-2.7%)	⬇️
internal/controllers/gateway/gateway_controller.go	66.8% <0.0%> (-1.2%)	⬇️
internal/controllers/gateway/gateway_utils.go	90.0% <0.0%> (-0.5%)	⬇️
internal/dataplane/parser/parser.go	89.7% <0.0%> (+0.6%)	⬆️
internal/dataplane/kongstate/service.go	67.3% <0.0%> (+1.2%)	⬆️
...nternal/controllers/gateway/tcproute_controller.go	75.6% <0.0%> (+2.6%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.