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

plugin/plugintest/api.go

@@ -223,6 +223,16 @@ func (m *API) UpdateChannel(channel *model.Channel) (*model.Channel, *model.AppE
 	return channelOut, err
 }
 
+func (m *API) AddChannelMember(channelId, userId string) (*model.ChannelMember, *model.AppError) {
+	ret := m.Called(channelId, userId)
+	if f, ok := ret.Get(0).(func(_, _ string) (*model.ChannelMember, *model.AppError)); ok {
+		return f(channelId, userId)
+	}
+	member, _ := ret.Get(0).(*model.ChannelMember)
+	err, _ := ret.Get(1).(*model.AppError)
+	return member, err
+}
+
 func (m *API) GetChannelMember(channelId, userId string) (*model.ChannelMember, *model.AppError) {
 	ret := m.Called(channelId, userId)
 	if f, ok := ret.Get(0).(func(_, _ string) (*model.ChannelMember, *model.AppError)); ok {
@@ -233,6 +243,35 @@ func (m *API) GetChannelMember(channelId, userId string) (*model.ChannelMember,
 	return member, err
 }
 
+func (m *API) UpdateChannelMemberRoles(channelId, userId, newRoles string) (*model.ChannelMember, *model.AppError) {
+	ret := m.Called(channelId, userId, newRoles)
+	if f, ok := ret.Get(0).(func(_, _, _ string) (*model.ChannelMember, *model.AppError)); ok {
+		return f(channelId, userId, newRoles)
+	}
+	member, _ := ret.Get(0).(*model.ChannelMember)
+	err, _ := ret.Get(1).(*model.AppError)
+	return member, err
+}
+
+func (m *API) UpdateChannelMemberNotifications(channelId, userId string, notifications map[string]string) (*model.ChannelMember, *model.AppError) {
+	ret := m.Called(channelId, userId, notifications)
+	if f, ok := ret.Get(0).(func(_, _ string, _ map[string]string) (*model.ChannelMember, *model.AppError)); ok {
+		return f(channelId, userId, notifications)
+	}
+	member, _ := ret.Get(0).(*model.ChannelMember)
+	err, _ := ret.Get(1).(*model.AppError)
+	return member, err
+}
+
+func (m *API) DeleteChannelMember(channelId, userId string) *model.AppError {
+	ret := m.Called(channelId, userId)
+	if f, ok := ret.Get(0).(func(_, _ string) *model.AppError); ok {
+		return f(channelId, userId)
+	}
+	err, _ := ret.Get(0).(*model.AppError)
+	return err
+}
+
 func (m *API) CreatePost(post *model.Post) (*model.Post, *model.AppError) {
 	ret := m.Called(post)
 	if f, ok := ret.Get(0).(func(*model.Post) (*model.Post, *model.AppError)); ok {