Ignore "@" sign at the beginning of user searches (#9780)

This trims the "@" symbol from the begging of the search term before executing the query.

store/sqlstore/user_store.go

@@ -1166,7 +1166,7 @@ func generateSearchQuery(searchQuery string, terms []string, fields []string, pa
 			}
 		}
 		searchTerms = append(searchTerms, fmt.Sprintf("(%s)", strings.Join(searchFields, " OR ")))
-		parameters[fmt.Sprintf("Term%d", i)] = fmt.Sprintf("%s%%", term)
+		parameters[fmt.Sprintf("Term%d", i)] = fmt.Sprintf("%s%%", strings.TrimLeft(term, "@"))
 	}
 
 	searchClause := strings.Join(searchTerms, " AND ")

store/storetest/user_store.go

@@ -1658,6 +1658,16 @@ func testUserStoreSearch(t *testing.T, ss store.Store) {
 			},
 			[]*model.User{u1},
 		},
+		{
+			"leading @ should be ignored",
+			tid,
+			"@jimb",
+			&model.UserSearchOptions{
+				AllowFullNames: true,
+				Limit:          model.USER_SEARCH_DEFAULT_LIMIT,
+			},
+			[]*model.User{u1},
+		},
 	}
 
 	for _, testCase := range testCases {