Pipeline editor: Replace the commit confirmation alert with a toast

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What does this MR do and why?

This MR aims to replace the commit confirmation alert in the pipeline editor with a toast message.

Closes: #345559 (closed)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Before	After
before.mov	after.mov

How to set up and validate locally

Verify the commit success message

1. Navigate to a project.
2. Add .gitlab-ci.yml (if it's not present).
3. Click on .gitlab-ci.yml, click on Edit choose Edit in pipeline editor .
4. Make some changes.
5. Click on Commit changes button.
6. The toast message should be displayed.

Verify the commit success message with a redirect

1. Navigate to a project.
2. Add .gitlab-ci.yml (if it's not present).
3. Click on .gitlab-ci.yml, click on Edit choose Edit in pipeline editor .
4. Make some changes.
5. In the Branch input, replace the default branch name with a new one.
6. Check Start a new merge request with these changes checkbox.
7. Click on Commit changes button.
8. The toast message should be displayed.

Note: on my videos there is a webpack error (I guess) on redirect. I think it's unrelated to the changes in this MR because it is also present on a pure master branch.