Show dismissal reason in pipeline security tab

What does this MR do and why?

Related #433336 (closed)

This shows the dismissal reason (if any) of dismissed findings in the table when the feature flag pipeline_security_dashboard_graphql is enabled on the pipeline security tab.

Screenshots or screen recordings

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Before	After

How to set up and validate locally

Prerequisites

1. You need an EE license
2. You need to have runners enabled (See $2408961 for setting up a runner)
3. Import https://gitlab.com/gitlab-examples/security/security-reports
4. Run a pipeline on master

Validation

1. Enable feature flag: echo "Feature.enable(:pipeline_security_dashboard_graphql)" | rails console
2. Go to the latest pipeline > security tab
3. Click on a finding
4. Click "Dismiss vulnerability" in the modal and select a dismissal reason
5. Click "Confirm dismissal"
6. Refresh page. Note: this will update automatically with #433509 (closed)
7. Filter status by "All dismissal reasons"
8. Validate you can see the finding you just dismissed with the dismissal reason badge

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.