docs: add a PR checklist template (#4564)

Manual testing of  this template can be done with the new playground created for that purpose, see https://code.forgejo.org/forgejo/pr-and-issue-templates/pulls/19.

![image](/attachments/1ee36ae1-669f-47d8-8307-9734faa0dc2a)

## Testing instructions

* Fork https://code.forgejo.org/forgejo/pr-and-issue-templates
* Create a pull request against https://code.forgejo.org/forgejo/pr-and-issue-templates
* See that the commit message is on top and the checklist below it

---

Use cases:

* https://codeberg.org/forgejo/forgejo/pulls/4553
* https://codeberg.org/forgejo/forgejo/pulls/4554

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/4564
Reviewed-by: 0ko <0ko@noreply.codeberg.org>
Reviewed-by: twenty-panda <twenty-panda@noreply.codeberg.org>
Reviewed-by: thefox <thefox@noreply.codeberg.org>
Co-authored-by: Earl Warren <contact@earl-warren.org>
Co-committed-by: Earl Warren <contact@earl-warren.org>

.forgejo/issue_template/bug-report-ui.yaml

@@ -0,0 +1,57 @@
+name: 🦋 Bug Report (web interface / frontend)
+description: Something doesn't look quite as it should?  Report it here!
+title: "bug: "
+labels: ["bug/new-report", "forgejo/ui"]
+body:
+- type: markdown
+  attributes:
+    value: |
+      **NOTE: If your issue is a security concern, please email <security@forgejo.org> (GPG: `A4676E79`) instead of opening a public issue.**
+- type: markdown
+  attributes:
+    value: |
+      - Please speak English, as this is the language all maintainers can speak and write.
+      - Be as clear and concise as possible. A very verbose report is harder to interpret in a concrete way.
+      - Be civil, and follow the [Forgejo Code of Conduct](https://codeberg.org/forgejo/code-of-conduct).
+      - Take a moment to [check that your issue hasn't been reported before](https://codeberg.org/forgejo/forgejo/issues?q=&type=all&labels=78137).
+- type: dropdown
+  id: can-reproduce
+  attributes:
+    label: Can you reproduce the bug on the Forgejo test instance?
+    description: |
+      Please try reproducing your issue at https://dev.next.forgejo.org.
+      It is running the latest development branch and will confirm the problem is not already fixed.
+      If you can reproduce it, provide a URL in the description.
+    options:
+    - "Yes"
+    - "No"
+  validations:
+    required: true
+- type: textarea
+  id: description
+  attributes:
+    label: Description
+    description: |
+      Please provide a description of your issue here, with a URL if you were able to reproduce the issue (see above).
+      If you think this is a JavaScript error, include a copy of the JavaScript console.
+  validations:
+    required: true
+- type: textarea
+  id: screenshots
+  attributes:
+    label: Screenshots
+    description: Please provide at least one screenshot showing the issue.
+  validations:
+    required: true
+- type: input
+  id: forgejo-ver
+  attributes:
+    label: Forgejo Version
+    description: Forgejo version (or commit reference) your instance is running
+- type: input
+  id: browser-ver
+  attributes:
+    label: Browser Version
+    description: The browser and version that you are using to access Forgejo
+  validations:
+    required: true