Performer urls (#4958)

* Populate URLs from legacy fields
* Return nil properly in xpath/json scrapers
* Improve migration logging

pkg/utils/url.go

@@ -0,0 +1,15 @@
+package utils
+
+import "regexp"
+
+// URLFromHandle adds the site URL to the input if the input is not already a URL
+// siteURL must not end with a slash
+func URLFromHandle(input string, siteURL string) string {
+	// if the input is already a URL, return it
+	re := regexp.MustCompile(`^https?://`)
+	if re.MatchString(input) {
+		return input
+	}
+
+	return siteURL + "/" + input
+}