Additional APIs for Focalboard multi-product architecture (#20608)

- adds HasPermissionToChannel to permissions service
- adds GetChannelsForTeamForUser to channel service

product/api.go

@@ -41,6 +41,7 @@ type PostService interface {
 // The service shall be registered via app.PermissionKey service key.
 type PermissionService interface {
 	HasPermissionToTeam(userID, teamID string, permission *model.Permission) bool
+	HasPermissionToChannel(askingUserID string, channelID string, permission *model.Permission) bool
 }
 
 // ClusterService enables to publish cluster events. In addition to that, It's being used for
@@ -61,6 +62,7 @@ type ChannelService interface {
 	GetDirectChannel(userID1, userID2 string) (*model.Channel, *model.AppError)
 	GetChannelByID(channelID string) (*model.Channel, *model.AppError)
 	GetChannelMember(channelID string, userID string) (*model.ChannelMember, *model.AppError)
+	GetChannelsForTeamForUser(teamID string, userID string, opts *model.ChannelSearchOpts) (model.ChannelList, *model.AppError)
 }
 
 // LicenseService provides license related utilities.