connector: first pass at bridging guilds

For each guild specified in the config, create a space and bridge all
contained text channels that the user has permissions to view.

* Finally add a custom config struct where we accept a list of guild IDs
  to bridge. This is intended to be temporary as we flesh out the proper
  interfaces for managing which guilds to bridge.
* Defined a custom meta type for portals that holds the containing guild
  ID of the channel (if any).
* Transferred the responsibility of building a channel's ChatInfo and
  ChatMemberList to the DiscordChatResync event itself.

pkg/connector/dbmeta.go

@@ -24,6 +24,9 @@ import (
 
 func (d *DiscordConnector) GetDBMetaTypes() database.MetaTypes {
 	return database.MetaTypes{
+		Portal: func() any {
+			return &discordid.PortalMetadata{}
+		},
 		UserLogin: func() any {
 			return &discordid.UserLoginMetadata{}
 		},