Add name field for org api (#21270)

related #21205

The field `UserName` is not really usefull for an organization.
This adds a second `Name` field.

The [GitHub API](https://docs.github.com/en/rest/orgs/orgs#get-an-organization) uses `name` too. `UserName` should be deprecated then.

modules/structs/org.go

@@ -7,7 +7,7 @@ package structs
 // Organization represents an organization
 type Organization struct {
 	ID                        int64  `json:"id"`
-	UserName                  string `json:"username"`
+	Name                      string `json:"name"`
 	FullName                  string `json:"full_name"`
 	AvatarURL                 string `json:"avatar_url"`
 	Description               string `json:"description"`
@@ -15,6 +15,8 @@ type Organization struct {
 	Location                  string `json:"location"`
 	Visibility                string `json:"visibility"`
 	RepoAdminChangeTeamAccess bool   `json:"repo_admin_change_team_access"`
+	// deprecated
+	UserName string `json:"username"`
 }
 
 // OrganizationPermissions list different users permissions on an organization