Add SubscribeAllEnvelopes endpoint to the Replication API

[Maelkum]

This PR introduces a new endpoint to the Replication API specification, allowing subscription to all envelopes, with a cursor to optionally specify starting point.

This is a somewhat distinct version of SubscribeEnvelopes, which mandates that either topics or originators are specified in the query filter.

This endpoint will be primarily (only) used by the notification server, and will have separate authorization and rate limit settings (details TBD).

Part of work on xmtp/example-notification-server-go#61

Note

Add SubscribeAllEnvelopes RPC endpoint to the Replication API

Adds a new SubscribeAllEnvelopes streaming RPC to the ReplicationApi service in message_api.proto, exposed as POST /mls/v2/subscribe-all-envelopes. The new SubscribeAllEnvelopesRequest message accepts an optional last_seen cursor to support resumable streaming, and returns a stream of SubscribeEnvelopesResponse messages.

^{Macroscope summarized 1565c0e.}

[Maelkum]

Return type is reused - shared with the SubscribeEnvelopes endpoint, since they return the same thing

[neekolas]

I do not believe subscribe all needs a cursor. We don't provide it in the V3 version and it is very expensive to deliver on.

If someone provides a cursor of 0 we are going to try and send them terrabytes of messages immediately.

[Maelkum]

I do not believe subscribe all needs a cursor. We don't provide it in the V3 version and it is very expensive to deliver on.

If someone provides a cursor of 0 we are going to try and send them terrabytes of messages immediately.

Makes sense, I created an issue to change that in a separate PR