MM-8678: add CUD support for channel members via plugins (#8565)

* add CUD support for channel members via plugins

This effectively exposes AddChannelMember, UpdateChannelMemberRoles,
UpdateChannelMemberNotifyProps and LeaveChannel via the plugin API.

It also modifies the semantics of AddChannelMember to explicitly allow
for an empty user requestor, left as such for now via the plugin API.

* change the signature of AddChannelMember to accept a channel id instead of a channel

app/plugin_api.go

@@ -124,10 +124,35 @@ func (api *PluginAPI) UpdateChannel(channel *model.Channel) (*model.Channel, *mo
 	return api.app.UpdateChannel(channel)
 }
 
+func (api *PluginAPI) AddChannelMember(channelId, userId string) (*model.ChannelMember, *model.AppError) {
+	// For now, don't allow overriding these via the plugin API.
+	userRequestorId := ""
+	postRootId := ""
+
+	channel, err := api.GetChannel(channelId)
+	if err != nil {
+		return nil, err
+	}
+
+	return api.app.AddChannelMember(userId, channel, userRequestorId, postRootId)
+}
+
 func (api *PluginAPI) GetChannelMember(channelId, userId string) (*model.ChannelMember, *model.AppError) {
 	return api.app.GetChannelMember(channelId, userId)
 }
 
+func (api *PluginAPI) UpdateChannelMemberRoles(channelId, userId, newRoles string) (*model.ChannelMember, *model.AppError) {
+	return api.app.UpdateChannelMemberRoles(channelId, userId, newRoles)
+}
+
+func (api *PluginAPI) UpdateChannelMemberNotifications(channelId, userId string, notifications map[string]string) (*model.ChannelMember, *model.AppError) {
+	return api.app.UpdateChannelMemberNotifyProps(notifications, channelId, userId)
+}
+
+func (api *PluginAPI) DeleteChannelMember(channelId, userId string) *model.AppError {
+	return api.app.LeaveChannel(channelId, userId)
+}
+
 func (api *PluginAPI) CreatePost(post *model.Post) (*model.Post, *model.AppError) {
 	return api.app.CreatePostMissingChannel(post, true)
 }