Feat: webhook push events edit form ui

What does this MR do and why?

MR made by @lxwan.

This is the frontend part of the issue #369104 (closed).

For the backend part, see: !97235 (merged)

In this MR, webhook push event allows regular expression as the match pattern to trigger the webhook.

/cc @prajnamas @orozot @qk44077907 @luzhiyuan.deer

Describe in detail what your merge request does and why.

Screenshots or screen recordings

Before change

After the change

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

How to set up and validate locally

1. Check out the backend branch, see: !97235 (merged)
2. Rebase the current branch on top of the backend branch.
3. Enable the feature flag introduced in the backend MR !97235 (merged).

Feature.enable(:enhanced_webhook_support_regex)

4. Go to GDK
5. Go to any project > Settings > Repository > Push rules > Webhook.
6. Try to interact with the new UI.

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

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