MM-27493 Shared channels (MVP) (#17301)

Remote Cluster Service
- provides ability for multiple Mattermost cluster instances to create a trusted connection with each other and exchange messages
- trusted connections are managed via slash commands (for now)
- facilitates features requiring inter-cluster communication, such as Shared Channels
Shared Channels Service
- provides ability to shared channels between one or more Mattermost cluster instances (using trusted connection)
- sharing/unsharing of channels is managed via slash commands (for now)

model/auditconv.go

@@ -51,6 +51,8 @@ func AuditModelTypeConv(val interface{}) (newVal interface{}, converted bool) {
 		return newAuditIncomingWebhook(v), true
 	case *OutgoingWebhook:
 		return newAuditOutgoingWebhook(v), true
+	case *RemoteCluster:
+		return newRemoteCluster(v), true
 	}
 	return val, false
 }
@@ -667,3 +669,42 @@ func (h auditOutgoingWebhook) MarshalJSONObject(enc *gojay.Encoder) {
 func (h auditOutgoingWebhook) IsNil() bool {
 	return false
 }
+
+type auditRemoteCluster struct {
+	RemoteId     string
+	RemoteTeamId string
+	DisplayName  string
+	SiteURL      string
+	CreateAt     int64
+	LastPingAt   int64
+	CreatorId    string
+}
+
+// newRemoteCluster creates a simplified representation of RemoteCluster for output to audit log.
+func newRemoteCluster(r *RemoteCluster) auditRemoteCluster {
+	var rc auditRemoteCluster
+	if r != nil {
+		rc.RemoteId = r.RemoteId
+		rc.RemoteTeamId = r.RemoteTeamId
+		rc.DisplayName = r.DisplayName
+		rc.SiteURL = r.SiteURL
+		rc.CreateAt = r.CreateAt
+		rc.LastPingAt = r.LastPingAt
+		rc.CreatorId = r.CreatorId
+	}
+	return rc
+}
+
+func (r auditRemoteCluster) MarshalJSONObject(enc *gojay.Encoder) {
+	enc.StringKey("remote_id", r.RemoteId)
+	enc.StringKey("remote_team_id", r.RemoteTeamId)
+	enc.StringKey("display_name", r.DisplayName)
+	enc.StringKey("site_url", r.SiteURL)
+	enc.Int64Key("create_at", r.CreateAt)
+	enc.Int64Key("last_ping_at", r.LastPingAt)
+	enc.StringKey("creator_id", r.CreatorId)
+}
+
+func (r auditRemoteCluster) IsNil() bool {
+	return false
+}