[skip ci] [WIP] Data access service in NP

[stacey-gammon]

[skip-ci] NP version of #38737

** Note the final PR will likely not have all the sample plugins.

Overview

Introduces two new extension points, one on the client side and one on the server side, both called Search strategies for now for lack of better terms.

New Plugins

search (OSS)

• New client side extension point, registerClientSearchStrategyProvider
• Way to expose custom information to the client side search strategy via registerSearchStrategyContext
• New server side extension point, addSearchStrategyProvider
  • Feel free to give naming feedback Should we call this registerSeverSearchStrategyProvider?
• A SYNC_SEARCH_STRATEGY, which does not handle querying anything itself, so it requires a serverStrategy attribute to know which backend to use.

es_search (OSS)

• Synchronous way to query elasticsearch via

context.search(
  { ...request, serverStrategy: ES_SEARCH_STRATEGY },
  { signal },
  SYNC_SEARCH_STRATEGY
)

• Only registers a server side search strategy.
• Uses the SYNC_SEARCH_STRATEGY on the client side.
• TODO: if it registers a client side search strategy we can simplify caller usage and only have them do:

context.search(request, { signal }, ES_SEARCH_STRATEGY)

which would just internally use the above code on the client side.

async_search (commercial)

• A client side only, commercial search strategy that handles asynchronous back ends, continuously querying until percentComplete reaches 100.
• TODO: use something other than percentComplete.

demo_data_search (sample plugin, relies on xpack plugin)

• Registers both client and server side search strategies.
• Doesn't hit ES at all but returns random data in an asynchronous manner.
• Depends on the ASYNC_SEARCH_STRATEGY plugin which is part of x-pack.

time_chunk_es_search (sample plugin, relies on xpack plugin)

• Registers both client and server side search strategies.
• Depends on the server side ES_SEARCH_STRATEGY plugin.
• Depends on the client side ASYNC_SEARCH_STRATEGY plugin which is part of x-pack.

kbn_tp_search_explorer (sample plugin)

A sample plugin with working examples, showcasing various plugins that extend and use the search plugin.

Playground

Run via yarn start --plugin-path test/plugin_functional/plugins/demo_data_search/ --plugin-path test/plugin_functional/plugins/kbn_tp_search_explorer/ --plugin-path test/plugin_functional/plugins/time_chunk_es_search to see the data explorer plugin.

Resolves #43371.

[stacey-gammon]

@joshdover here is where I'm doing the bad things :)

[elasticmachine]

Pinging @elastic/kibana-app-arch (Team:AppArch)