PLT-3762 - Add API call to get a user by their username (#4611)

* PLT-3762 - Add API call to get a user by their username

* fix lint

* update rote

* update per code review

* update per code review

* remove first/last name is not used in this test

model/client.go

@@ -500,6 +500,17 @@ func (c *Client) GetUser(id string, etag string) (*Result, *AppError) {
 	}
 }
 
+// getByUsername returns a user based on a provided username string. Must be authenticated.
+func (c *Client) GetByUsername(username string, etag string) (*Result, *AppError) {
+	if r, err := c.DoApiGet(fmt.Sprintf("/users/name/%v", username), "", etag); err != nil {
+		return nil, err
+	} else {
+		defer closeBody(r)
+		return &Result{r.Header.Get(HEADER_REQUEST_ID),
+			r.Header.Get(HEADER_ETAG_SERVER), UserFromJson(r.Body)}, nil
+	}
+}
+
 // GetMe returns the current user.
 func (c *Client) GetMe(etag string) (*Result, *AppError) {
 	if r, err := c.DoApiGet("/users/me", "", etag); err != nil {