Added a GitHub pull request template.

Co-authored-by: Natalia <124304+nessita@users.noreply.github.com>
Co-authored-by: Paolo Melchiorre <paolo@melchiorre.org>
Co-authored-by: Adam Johnson <me@adamj.eu>

.github/pull_request_template.md

@@ -0,0 +1,15 @@
+# Trac ticket number
+<!-- Replace [number] with the corresponding Trac ticket number, or delete the line and write "N/A" if this is a trivial PR. -->
+
+ticket-[number]
+
+# Branch description
+Provide a concise overview of the issue or rationale behind the proposed changes.
+
+# Checklist
+- [ ] This PR targets the `main` branch. <!-- Backports will be evaluated and done by mergers, when necessary. -->
+- [ ] The commit message is written in past tense, mentions the ticket number, and ends with a period.
+- [ ] I have checked the "Has patch" **ticket flag** in the Trac system.
+- [ ] I have added or updated relevant **tests**.
+- [ ] I have added or updated relevant **docs**, including release notes if applicable.
+- [ ] For UI changes, I have attached **screenshots** in both light and dark modes.