[MM-13746] Add GetTeamMembersForUser and GetChannelMembersForUser apis (#10269)

* Add GetTeamMembersForUser and GetChannelMembersForUser apis

* Address comments

* Fix tests

* Fix test

* Fix comment

* Fix minimum server version

* Change to []*model.ChannelMember

* Fix panic, add more tests

* Remove print statement

plugin/api.go

@@ -174,6 +174,11 @@ type API interface {
 	// GetTeamMember returns a specific membership.
 	GetTeamMember(teamId, userId string) (*model.TeamMember, *model.AppError)
 
+	// GetTeamMembersForUser returns all team memberships for a user.
+	//
+	// Minimum server version: 5.10
+	GetTeamMembersForUser(userId string, page int, perPage int) ([]*model.TeamMember, *model.AppError)
+
 	// UpdateTeamMemberRoles updates the role for a team membership.
 	UpdateTeamMemberRoles(teamId, userId, newRoles string) (*model.TeamMember, *model.AppError)
 
@@ -247,6 +252,11 @@ type API interface {
 	// Minimum server version: 5.6
 	GetChannelMembersByIds(channelId string, userIds []string) (*model.ChannelMembers, *model.AppError)
 
+	// GetChannelMembersForUser returns all channel memberships on a team for a user.
+	//
+	// Minimum server version: 5.10
+	GetChannelMembersForUser(teamId, userId string, page, perPage int) ([]*model.ChannelMember, *model.AppError)
+
 	// UpdateChannelMemberRoles updates a user's roles for a channel.
 	UpdateChannelMemberRoles(channelId, userId, newRoles string) (*model.ChannelMember, *model.AppError)