Display correct message based on action

What does this MR do and why?

Displays the correct toaster message based on the action. If edited, it now displays Comment edited on, if added, it displays Comment added on.

Screenshots or screen recordings

How to set up and validate locally

1. You'll need an EE License
2. You'll need to have runners enabled (See $2408961 for setting up a runner)
3. Enable :refactor_security_extension to turn this feature on.

echo "Feature.enable(:refactor_security_extension)" | rails c

Steps:

1. Import https://gitlab.com/gitlab-examples/security/security-reports
2. Create a new MR by modifying a file
3. Toggle security reports
4. Click on a finding
5. Add a dismissal comment or edit one
6. Check that the toaster message is correct

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 #386009 (closed)