Revisit webhook rate limit feature flags for application settings conversion
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## Context
This issue tracks the evaluation and potential refactoring of two webhook rate limit feature flags:
- `web_hook_event_resend_api_endpoint_rate_limit`
- `web_hook_test_api_endpoint_rate_limit`
## Motivation
As noted in MR !218726, these ops feature flags should be evaluated for conversion to application settings instead of remaining as long-lived feature flags.
### Suggestions from Review
From @SamWord's review comments:
> "I'm not really sure why this needs to be an ops flag when we could make the webhook resend API rate limit configurable in application settings"
> "This flag functions the same as `web_hook_event_resend_api_endpoint_rate_limit` but for a different rate limit. I also don't see why this shouldn't be a rate limit that's configurable in application settings"
## Proposal
Convert these webhook rate limit feature flags to configurable application settings, allowing administrators to adjust rate limits without requiring feature flag changes.
## Related
- MR: !218726 - Refresh milestone for Import ops feature flags
- Feature flag documentation: https://docs.gitlab.com/development/feature_flags/#ops-type
issue