[MM-47024][MM-47708] Create remote entrypoint for webapp to be imported by desktop, add basic module registry

[devinbinnie]

Summary

This is the beginning of the work to allow the Web App to be consumed as a module by the Desktop App.

We use Module Federation to expose a remoteEntry.js file that the Desktop App will pick up and read. That file exposes certain entry points for the Desktop App to load and use as it sees fit. Right now we are only exposing the Redux Store, the styles, and the root component.

In order to allow for overrides, I've added a super basic module registry that is also exposed to the Desktop App. This allows the Desktop App to override any module that is marked as effectively "overridable" in the Web App.

This is still a WIP, but I'm keeping it up here so that development on this can be tracked as it goes.

Ticket Link

https://mattermost.atlassian.net/browse/MM-47024

Related Pull Requests

Desktop PR: coming soon

NONE

[devinbinnie]

@hmhealey Ready for another pass.

[hmhealey]

https://github.com/mattermost/desktop/pull/2343