Discover Code loading race condition with embeddables

[flash1293]

Kibana version: 7.8

Describe the bug: In some cases the "search" embeddable is registered too late, causing the embeddable to fail to render in a dashboard.

Steps to reproduce:
Put a saved search on a dashboard and reload (multiple times). This depends on the specific timing of requests

Seen here:
https://discuss.elastic.co/t/embeddable-factory-embeddablefactoryid-search-does-not-exist/239270

Expected behavior:

The search embeddable should always be registered in the setup phase with async steps.

Any additional context:

This can happen because code is loaded async before the embeddable is registered:

kibana/src/plugins/discover/public/plugin.ts

Line 350 in 684aa68

plugins: DiscoverSetupPlugins

This means it's not registered in the setup phase and can leak into the start phase. We should register the factory during setup, then load the actual embeddable and other stuff async when it's used the first time.

[kertal]

dear @flash1293 , totally makes sense, working on a fix in #70920. one question, could you reproduce it locally? thx!

[flash1293]

@kertal I couldn't reproduce so far, but it should be easy to enforce by putting a long running await in front of the dynamic import to simulate a delay in loading this bundle.

Like function delay() { return new Promise((resolve) => { setTimeout(resolve, 5000) }) } await delay().