chore: Add error-report issue template

The `error-report` label was not being added to error reports
submitted by panics in the web player, despite the `labels` query
parameter in the URL. Users do not have triage/write access to the
repo, which is required by GitHub to add a label to an issue.

Add an issue template for error reports with the `error-report`
label. This template is now added to the issue URL, which
automatically adds the tag regardless of access level.

.github/ISSUE_TEMPLATE/error_report.md

@@ -0,0 +1,7 @@
+---
+name: Error report
+title: "Error"
+about:
+labels: ["error-report"]
+assignees: ""
+---

web/packages/core/src/ruffle-player.ts

@@ -1127,7 +1127,7 @@ export class RufflePlayer extends HTMLElement {
         const issueTitle = `Error on ${pageUrl}`;
         let issueLink = `https://github.com/ruffle-rs/ruffle/issues/new?title=${encodeURIComponent(
             issueTitle
-        )}&labels=error-report&body=`;
+        )}&template=error_report.md&labels=error-report&body=`;
         let issueBody = encodeURIComponent(errorText);
         if (
             errorArray.stackIndex > -1 &&