Add snowplow tracking to report abuse form

What does this MR do and why?

This adds backend Snowplow tracking for the Report Abuse form. We want to track the percentage of reports by category and the percentage of reports that get started versus that get submitted.

The following events are tracked:

1. An abuse category is selected

   se_category: "ReportAbuse",
   se_action: "select_abuse_category",
   se_property: "spam",

2. The form is submitted

   se_category: "ReportAbuse",
   se_action: "submit_form",
   se_property: "spam",

Screenshots or screen recordings

select_abuse_category	submit_form

How to set up and validate locally

1. Install Snowplow micro

   gdk config set snowplow_micro.enabled true
   gdk reconfigure

2. Navigate to an issue created by another user, click on ︙ > Report abuse to administrator

3. Visit http://localhost:9091/micro/good to check that all events are tracked.

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.

Resolves https://gitlab.com/gitlab-org/modelops/anti-abuse/team-tasks/-/issues/194