refactor(getters/shrex): construct peer manager inside shrex-getter

[distractedm1nd]

          If ShrexGetter maintains the lifecycle of `peer.Manager`, it should also construct it, i.e. `peer.Manager` is a child of ShrexGetter but not a dependency. This also means that peer manager won't be part of FX dep graph, which is totally ok as the peer manager is singly purposed.

Originally posted by @Wondertan in https://github.com/celestiaorg/celestia-node/pull/1743#discussion_r1105906346

[walldiss]

@renaynay Please add more details on impl details