[Fleet] Add UI integration tests for Integrations app

[joshdover]

We need to add e2e tests for several key flows in the integrations app. This is critical as this app is now the main entry point for new users and we need to be sure that it doesn't break. Follow up to #93084

These should be added to Fleet's cypress suite in https://github.com/elastic/kibana/tree/main/x-pack/test/fleet_cypress

Key flows that need tests, in rough priority order:

• [ ] Clicking on key "add integration" links in Kibana should render the integrations app
  • [ ] "Add integration" button in main nav drawer
  • [ ] Welcome interstitial
  • [ ] Primary call out on home app
  • [ ] Observability empty state UI
  • [ ] Security empty state UI
• [ ] Clicking a beats card should render the corresponding beats tutorial
• [ ] Clicking an EPR card should render the integration details view
• [ ] Clicking the sample data card should render the sample data UI
• [ ] Clicking the file upload card should render the file upload UI
• [ ] Clicking a category should filter the list
• [ ] Typing into the search bar while in a category should switch the selected category to 'all'
• [ ] Choosing a preferred shipper should filter other cards
  • [ ] Choosing "Elastic Agent" should hide all Beats tutorials
  • [ ] Choosing "Beats" should hide all Elastic Agent integrations
  • [ ] Choosing "Recommended" should prefer Elastic Agent
    • We need to be sure this test is not affected by EPR updates. It probably makes sense to add a test package for the local test EPR instance that overrides one of the existing integrations and sets it to 'beta' so that we can test this behavior.
• [ ] Users with only read access should be able to visit the app and view integrations, but not install them

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[joshdover]

cc @alexfrancoeur @mostlyjason Does this priority make sense? Any key flows that are missing here?