Add pull-request template (#1777)

While @kevinjqliu did an amazing job summarizing the new stuff in 0.9.0
in the GitHub release
(https://github.com/apache/iceberg-python/releases/tag/pyiceberg-0.9.0),
I think it would be good to formalize this a bit.

This also came up in #1669
where we introduced a behavioral change. cc @sungwy

I think it would be good to allow users to populate the changelog
section to ensure they know about any relevant changes.

The template is pretty minimal now to avoid being a big barrier to
opening a PR.

Author: Fokko

.github/pull_request_template.md

@@ -0,0 +1,14 @@
+<!--
+Thanks for opening a pull request!
+-->
+
+<!-- In the case this PR will resolve an issue, please replace ${GITHUB_ISSUE_ID} below with the actual Github issue id. -->
+<!-- Closes #${GITHUB_ISSUE_ID} -->
+
+# Rationale for this change
+
+# Are these changes tested?
+
+# Are there any user-facing changes?
+
+<!-- In the case of user-facing changes, please add the changelog label. -->

dev/.rat-excludes

@@ -1,3 +1,4 @@
+.github/*
 .rat-excludes
 build
 .git

mkdocs/docs/how-to-release.md

@@ -379,6 +379,8 @@ Then, select the previous release version as the **Previous tag** to use the dif
 
 **Set as the latest release** and **Publish**.
 
+Make sure to check the `changelog` label on GitHub to see if anything needs to be highlighted.
+
 ### Release the docs
 
 Run the [`Release Docs` Github Action](https://github.com/apache/iceberg-python/actions/workflows/python-release-docs.yml).