[REA-1702] feat: web push

[owenpearson]

• adds a plugin which enables clients to be activated for receipt of push notifications.
• adds support for w3c push transport to web clients.
• adds push channel transport for testing push activation on all platforms.

[ttypic]

Looks good! very consistent to what we have in java and cocoa, added couple of small comments

[VeskeR]

Have a wall of comments but mostly they are structural suggestions.

Couple of things that I couldn't attach to code lines:

1. Should we add new Push plugin to scripts/moduleReport.ts pluginNames list? I imagine we would need to update getBundleInfo in there, as currently it always imports from './build/modular/index.mjs'.
2. Per RSH7 both RestChannel and RealtimeChannel should have push object. Why did we add push only to RestChannel here?

P.S. sorry for the amount of comments 😬 I wonder if we could've done it in separate PRs for web push integration branch.

[VeskeR]

Great changes!
Really like the new classes for states! Looks much better and is easier to read.

Added couple more comments (and had to unresolve two previous comments I think), but we're really close now

[VeskeR]

LGTM!

[ttypic]

LGTM