InfluxDB: Fix regular expression to parse aliases according to documentation (#41186) (#41190)

* Fix regular expression to parse aliases that start with either square brackets or dollar sign

* Fix lint

(cherry picked from commit 8a3e192e6a)

Co-authored-by: Dimitris Sotirakis <dimitrios.sotirakis@grafana.com>

pkg/tsdb/influxdb/response_parser.go

@@ -16,7 +16,7 @@ import (
 type ResponseParser struct{}
 
 var (
-	legendFormat = regexp.MustCompile(`\[\[([\@\/\w-]+)(\.[\@\/\w-]+)*\]\]*|(\$*([\@\w-]+?))*`)
+	legendFormat = regexp.MustCompile(`\[\[([\@\/\w-]+)(\.[\@\/\w-]+)*\]\]*|\$(\s*([\@\w-]+?))*`)
 )
 
 func (rp *ResponseParser) Parse(buf io.ReadCloser, query *Query) *backend.QueryDataResponse {