Fix add/edit/delete dismissal comment for pipeline security tab

What does this MR do and why?

This MR updates the add/edit/delete dismissal comment actions on the pipeline security tab to use a GraphQL mutation instead of the vulnerability_feedback endpoint, which is going away as part of the deprecate vulnerabilities feedback work. The add/edit/delete dismissal comment feature can be done on the finding modal:

How to set up and validate locally

1. Disable the deprecate_vulnerabilities_feedback feature flag.
2. Clone any project that has security findings, like this one: https://gitlab.com/gitlab-examples/security/security-reports
3. Run a pipeline against any branch, then go to the pipeline security tab for that pipeline.
4. Click on a finding to open the modal.
5. Dismiss the finding with a comment, re-open the modal, and verify that the comment was added.
6. Re-open the modal, edit the comment, save it, re-open the modal, and verify that the comment was edited.
7. Re-open the modal, delete the comment, re-open the modal, and verify that the comment was removed.
8. Enable the deprecate_vulnerabilities_feedback feature flag and repeat steps 4-8.

Feature flag off

Feature flag on

MR acceptance checklist

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

• I have evaluated the MR acceptance checklist for this MR.

Related to #390073 (closed)