Stream inspector for destinations

[hariso]

Description

Depends on #732
Fixes #700

Quick checks:

• I have followed the Code Guidelines.
• There is no other pull request for the same update/change.
• I have written unit tests.
• I have made sure that the PR is of reasonable size and can be easily reviewed.

[lovromazgon]

I tried it out and it worked, both through a websocket and gRPC, nice work! I think the PR needs some polish but we're definitely on the right track 🙌

Some comments that don't belong anywhere else:

• Stopping Conduit with an inspector is not possible, Conduit blocks until the client closes the connection.
• It's possible to start an inspector on a stopped pipeline, we should probably check the status and return an error if that's the case.
• Similarly it's possible to stop a pipeline and keep an inspector running, I'd also expect the inspector to stop in that case.
• While testing I was able to process up to 120 records per second (I used https://websocketking.com/), that feels a bit slow given that it's running on the same machine, am I expecting too much?
• I don't think we mentioned metrics in the design, but I think it would be nice to at least see the number of open inspector sessions on a connector / processor. WDYT? No need to do it in this PR.

[lovromazgon]

Mostly just nitpicks, I think this is already looking very nice!

[lovromazgon]

LGTM 👏