add client4 apis needed for jira plugin (#7292)

plugin/api.go

@@ -1,7 +1,23 @@
 package plugin
 
+import (
+	"github.com/mattermost/platform/model"
+)
+
 type API interface {
 	// LoadPluginConfiguration loads the plugin's configuration. dest should be a pointer to a
 	// struct that the configuration JSON can be unmarshalled to.
 	LoadPluginConfiguration(dest interface{}) error
+
+	// GetTeamByName gets a team by its name.
+	GetTeamByName(name string) (*model.Team, *model.AppError)
+
+	// GetUserByUsername gets a user by their username.
+	GetUserByUsername(name string) (*model.User, *model.AppError)
+
+	// GetChannelByName gets a channel by its name.
+	GetChannelByName(name, teamId string) (*model.Channel, *model.AppError)
+
+	// CreatePost creates a post.
+	CreatePost(post *model.Post) (*model.Post, *model.AppError)
 }