* Revert "Moved subscribe and filter into network controller (#16693)"
This reverts commit 6f6984fa58. That
commit was an RPC middleware refactor intended to move the subscribe
and filter middleware into the network controller, to simplify the
process of sharing this middleware between clients.
This refactor resulted in `eth_subscribe` notifications being sent on
the wrong connections, causing the UI to break in some cases (the UI
`provider` connection does not support notifications). This happened
because the `setupProviderEngine` function runs per-connection,
whereas the engine setup inside the network controller is global. The
global network client cannot support notifications because it has no
way to route them; they'll need to stay in the per-connection provider
engine.
Closes#17467
* Add e2e test
An e2e test has been added that confirms subscriptions are only
broadcast to the site that registered them. This test fails on
`develop`.
