Kibana Platform plugins cannot access available features in start method

[azasypkin]

Summary

Currently if KP plugin accesses available features in its start method (via features.getFeatures()) it breaks legacy plugins that try to register new features since feature registry is frozen as soon as it's accessed for the first time (e.g XPack Main plugin registers all OSS features in its init method).

This issue turned out to be blocking migration of the Security plugin to Kibana Platform since in start method we need to access all available features, validate feature privileges and register these privileges with Elasticsearch.

[elasticmachine]

Pinging @elastic/kibana-platform (Team:Platform)

[mshustov]

we still register legacy features

kibana/x-pack/legacy/plugins/xpack_main/index.js

Lines 67 to 70 in a729b3b

	featuresPlugin.registerLegacyAPI({
	xpackInfo: setupXPackMain(server),
	savedObjectTypes: server.savedObjects.types,
	});

in x-pack_main plugin

kibana/x-pack/plugins/features/server/plugin.ts

Lines 81 to 91 in ee270c7

	registerLegacyAPI: (legacyAPI: LegacyAPI) => {
	this.legacyAPI = legacyAPI;
	// Register OSS features.
	for (const feature of buildOSSFeatures({
	savedObjectTypes: this.legacyAPI.savedObjectTypes,
	includeTimelion: visTypeTimelion !== undefined && visTypeTimelion.uiEnabled,
	})) {
	this.featureRegistry.register(feature);
	}
	},

[mshustov]

It's currently blocked by timelion and maps SO registration in the LP.
@joshdover it seems we have to push for timelion migration.

[mshustov]

blocked by #66203 and #66057

[joshdover]

It's currently blocked by timelion and maps SO registration in the LP.
@joshdover it seems we have to push for timelion migration.

Can we just migrate the SO registration for now?

[mshustov]

@joshdover yes, I ended up with it. forgot to update the comment #66203