Fix bug and improve access token expiration Webhooks UI

What does this MR do and why?

Flagged by the localization (translation team) in: https://gitlab.com/gitlab-com/localization/tech-docs-forked-projects/prod/gitlab/-/merge_requests/616#note_2857325343

While looking into the docs for this, we first realized that the docs and UI were out of sync. But the more I dug into it, the more issues I found:

• As mentioned, the UI text and docs did not match (as found by translators)
• The UI text could be simplified to avoid such a long compound noun (recommended by translators), but also simplified in general for clarity.
• The help text doesn't need links to docs that simply explain how to get back to the settings page you are already at.
• Most important The project setting itself seems to have a bug and does not show up. I suspect it's leftover feature flag code that was not removed when the feature flag was removed in: !184300 (merged)

References

• Related to Extend webhook notifications for expiring token... (#499732 - closed)
• Related to [Feature flag] Rollout of `extended_expiry_webh... (#513684 - closed)

Screenshots or screen recordings

Group settings:

• Before

  

• After

  

Project settings:

• Before (MISSING)

  

• After setting fixed (v-if="glFeatures.extendedExpiryWebhookExecutionSetting" removed)

  

• After UI updated

  

How to set up and validate locally

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