refactor(pd): 🎬 pull grpc endpoint into penumbra-app

[cratelyn]

see #3913, #3973 and #3588. this is a second attempt, following up on #3980.

🔭 background

NB: the difference between this and #3679 is that the latter (which ran afoul of a regression) would have penumbra-app create a Routes, that we would add to the builder (which stays in pd). here, i'm not trying to make that cut between Router and Routes, and am attempting to hoist the whole thing out of pd, without making changes to how we interact with tonic. my aim is for us to be able to move this, without running into that bug (#3697) again.

NB: after running into problems in #3980, i found a way to easily reproduce the issue locally. my belief was that something related to our dependencies' cargo features was at play. rather than isolate the issue, it was easier to rewrite this (it's just code motion, after all) while running some of the network integration tests in a loop.

unlike #3980, this moves the rpc server into penumbra-app, per #3980 (comment)

👁️ overview

we would like to use the rust view server in mock consensus tests. in order to run the penumbra_view::ViewServer however, we need to spin up the corresponding grpc endpoint for it to connect to.

this branch performs a bit of code motion, moving the grpc_server out of pd and into penumbra-app. there will likely be other functional changes to the code in question before we can use it in those tests, but this PR is interested in moving that code into a place where our tests can rely upon it.