Add App Search engines as non-Fleet integrations

[alexfrancoeur]

We would like to unify all ingestion capabilities from a single integrations page (#93084). As part of building a unified view, we'll need to navigate to App Search ingestion instructions.

After speaking with @bhuvanaurora and @zumwalt, we decided that we want to show each ingestion method as a card in the integrations page (potentially a subset). The current flow today enforces you to name an engine and then select an ingestion method. The flow we'd like to see incorporated would look something like the mockups below, directly navigating to the end destination after naming your engine.

One solution proposed was to persist a deep link to the ingestion instructions during the engine naming step. Alternatively, we could only show a single card for "app search" and keep the same. For discoverability purposed, we'd ideally like to show each option available to new users up front in the integrations page. Timeline wise, we would like to implement #93084 in 7.last and would like to explore solutions for the app search flows.

@bhuvanaurora and @zumwalt would you mind roping in the appropriate folks on the Enterprise Search team?

cc: @mostlyjason @dborodyansky

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[elasticmachine]

Pinging @elastic/app-search-frontend (Team:AppSearch)

[alexfrancoeur]

Opened an issue to track reduced scope work for MVP: #113825

[alexfrancoeur]

Tracking work for this effort in https://github.com/elastic/app-search-team/issues/1995

[snide]

This is closable now that https://github.com/elastic/app-search-team/issues/1995 is in.