Search for streamed audit event filter options in the UI to allow for easy filtering

Problem to solve

In Screen to allow management of streamed audit ev... (#344846 - closed) the frontend is being added to display a simple list of available filter options that it fetches from API to allow streamed audit events to be filter... (#344845 - closed). This list could be difficult to parse due to the length and similar names.

Proposal

It would be a nice quality of life improvement if the user could search for the filter they want to apply.

• The search would limit which options render based on if they match the input.

Design

Note: Implement with GlCollapsibleListbox instead of the current GlFormCheckboxTree because the listbox combines multiple selection, grouping, and searching in 1 component.

Full page example	changes in this issue

Implementation

GlCollapsibleListbox search documentation

• In stream_filters.vue, add new data property searchTerm and set this based on the search event of the GlCollapsibleListbox
• set searchable property on the GlCollapsibleListbox
• Filter items passed to GlCollapsibleListbox based on this searchTerm
• Update spec with tests for search

Verification steps

• Go to https://gitlab.com/groups/issue-reproduce/-/audit_events?tab=streams
• Expand the stream destination
• Select "Stream by filter event"
• Select "Select events" dropdown
• Verify that if no search term is provided, all audit event types are listed
• Verify that searching for audit event type properly filters the list
• Verify that the filtering is case-insensitive, by e.g. searching for "GPG". It should still show "Add gpg key" and "Remove gpg key" events