[New Platform] Expose uiSettings on server side

[stacey-gammon]

Plan

• migrate service tests to TypeScript. Convert uiSettings tests to TypeScript #46776
• migrate service code to TypeScript. Convert uiSettings service to TypeScript #47018
• move uiSettings to the new platform and provide API for plugins to register defaultUiSettings
• integrate uiSettings in the Legacy platform. Add validation that defaultUiSettings do not overwrite each other. UI settings move to NP #47590
• move uiSettings routes to the NP
• unify server side/client side interfaces Unify uiSettingsClient contracts #51167
• update docs with example how to switch from uiExports Unify uiSettingsClient contracts #51167

Nice to do:

• adopt service tests for the modern infrastructure. get rid of sinon, expect. update testing infrastructure for ui_settings #51266
• convert integration tests to the functional. Convert uiSettings tests to TypeScript #46776 (comment)
• introduce validator Support validation for UI Settings #46717
• get rid of defaults term as non-descriptive UI settings move to NP #47590 (comment)

Original post:
uiSettings is available on core in client side, but I think it makes sense to expose a similar service server side. The data plugin could use it, we'd like users to be able to use the search API, and if they leave certain settings off, we'll default to the ones in uiSettings.

cc @lukasolson

[elasticmachine]

Pinging @elastic/kibana-platform

[stacey-gammon]

Needed for #29215

[joshdover]

Related: #22779

[flash1293]

Needed for migrating the Graph server APIs

[rudolf]

There are a couple of existing plugins that would also be blocked by this (graph, siem, infra, dashboard_mode)

The server UISettingsClient will have to be exposed through the request context and use the request scoped SavedObjectsClient so that advanced settings remain space aware.

[joshdover]

@rudolf to be clear, this is blocked by #44143, correct?

[rudolf]

Correct.

[mshustov]

also blocked by #44983
https://github.com/restrry/kibana/blob/8170a02235ef9f3c54da5ba12aa331ee3a51627c/src/legacy/ui/ui_settings/ui_settings_service_factory.js#L50

[mshustov]

As the very first step, we can migrate legacy service to TypeScript. If SavedObjects and Logging with metadata aren't available soon, we can hack and provide legacy service via RequestHandlerContext using Legacy API. There is an example how to make it work in my branch master...restrry:expose-hacked-ui-settings

[joshdover]

We haven't prioritized logging metadata very high in our backlog. Maybe we need to re-evaluate? Do you know what else needs that feature?

[mshustov]

We haven't prioritized logging metadata very high in our backlog. Maybe we need to re-evaluate? Do you know what else needs that feature?

Only Security & Spaces plugins waits for it, other calls are done by the platform & optimizer.
All in all, it shouldn't take a lot of time to add metadata support. If it can be done in a day or so, we can prioritize it higher.

[mshustov]

minimum functionality is implemented. possible improvements are moved to #48925