Custom SW filename (#175)

* embed: support using custom filename for service worker instead of sw.js
can be set via <replay-web-page swName='custom.js' ... > property
docs: update embedding docs to mention new option
fixes #160

src/embed.js

@@ -247,6 +247,11 @@ class Embed extends LitElement
         params.loading = "eager";
       }
 
+      // eslint-disable-next-line no-undef
+      if (this.swName !== __SW_NAME__) {
+        params.swName = this.swName;
+      }
+
       this.paramString = new URLSearchParams(params).toString();
 
       this.hashString = new URLSearchParams({