Add dismissal descriptions to pipeline tabs dataset

What does this MR do and why?

Related to #422845 (closed)

In Provide and edit dismissal reason in finding modal (!130193 - merged) • Lorenz van Herwaarden • 16.4 we're adding a dismissal reason dropdown to select the reason of dismissal for a finding. For each dismissal reason, there are extended descriptions that explain why the reason would be applicable. We want to show these extended descriptions in tooltips in this new dismissal reason dropdown (see #422845 (closed)).

In the same way as this was done for the vulnerability details page (see ee/app/helpers/vulnerabilities_helper.rb), we want to pass these descriptions from the backend to the frontend via HAML.

This MR handles the backend part of #422845 (closed).

How to set up and validate locally

Run spec

1. bin/rspec ee/spec/helpers/ee/projects/pipeline_helper_spec.rb

Find data in container

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
5. go to security reports security pipeline: http://gdk.test:3000/root/security-reports/-/pipelines/1/security
6. (on chrome): right-click on page > view page source
7. find div with id: js-pipeline-tabs and check that is has an attribute data-dismissal-descriptions with the dismissal descriptions in json string

MR acceptance checklist

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