Add Pull Request Template (#5735)

It provides some useful information about what to take into account
when submitting a PR.

Co-authored-by: Kevin Wittek <kiview@users.noreply.github.com>

.github/pull_request_template.md

@@ -0,0 +1,19 @@
+<!--
+Thanks for contributing to Testcontainers. Please review the following notes before
+submitting a pull request.
+
+New Modules:
+Make sure to add it to `bug_report.yaml`, `enhancement.yaml` and `feature.yaml`.
+Also, add it to `dependabot.yml` and `labeler.yml`.
+
+Before comitting, run `./gradlew checkstyleMain checkstyleTest spotlessApply` and fix any issues that occur.
+
+Describing Your Changes:
+
+If, after having reviewed the notes above, you're ready to submit your pull request, please
+provide a brief description of the proposed changes and their context. If they fix a bug, please
+describe the broken behaviour and how the changes fix it. If they make an enhancement,
+please describe the new functionality and why you believe it's useful. If your pull
+request relates to any existing issues, please reference them by using the issue number
+prefixed with #.
+-->