Frontend: Event tracking for viewing agent and flow catalog

About

The backend is starting to add event tracking for GraphQL mutations in #553157 (closed).

We want to track the frontend -specific event of "viewing" the catalog #553157 (comment 2623139654).

We only need to track the view events because create, update and delete events are be tracked on the backend.

Proposal

The events would be:

• View agent catalog index
• View flow catalog index
• View an agent
• View a flow

See:

• Add event tracking when flows and agents are cr... (#553157 - closed) for the event structure and the associated backend implementation MR !198512 (merged)
• https://docs.gitlab.com/development/internal_analytics/internal_event_instrumentation/quick_start/

this.trackEvent('view_ai_catalog_item_index', { label: <flow/agent>}););
this.trackEvent('view_ai_catalog_item', { label: <flow/agent> });