[NEOS-758] Replace known host public key with known host public keys

[nickzelei]

We should support multiple public keys for a SSH tunnel server instead of one.

This is because a server is able to present multiple keys depending on what the client is able to support.

Since people don't know what we can support, we should allow them to give us multiple keys, and then we can try each one during the presentation.

Right now it's a little weird because they might give us one of the keys but that one may never be presented so it won't work on our server, and they have to keep trying the list of keys untl; they find one that neosync can use to successfully connect to.

This is also helpful if they are rotating their public keys and want us to have overlap in what we are expecting.

We should deprecate the existing known host field in the proto and db layer in favor of a repeated known hosts field.

The DB layer should merge the two during the DTO phase so that eventually, the single will get migrated to the list on next save.

_{From SyncLinear.com | NEOS-758}