Improve: Support search and adding federated users through regular endpoints (#13936)

app/federation/server/PeerClient.js

app/federation/server/PeerDNS.js

app/federation/server/PeerHTTP/PeerHTTP.js

app/federation/server/PeerHTTP/index.js

app/federation/server/PeerHTTP/utils.js

app/federation/server/PeerServer/PeerServer.js

app/federation/server/PeerServer/index.js

app/federation/server/PeerServer/routes/events.js

app/federation/server/PeerServer/routes/uploads.js

app/federation/server/PeerServer/routes/users.js

app/federation/server/federatedResources/FederatedMessage.js

...federation/server/federatedResources/FederatedResource.js

app/federation/server/federatedResources/FederatedRoom.js

app/federation/server/federatedResources/FederatedUser.js

app/federation/server/federatedResources/index.js

app/federation/server/index.js

app/federation/server/methods/addUser.js

app/federation/server/methods/federationAddUser.js

app/federation/server/methods/federationSearchUsers.js

app/federation/server/methods/index.js