chore: add client pull requests to pull request template

[matthewwalsh0]

Explanation

Update pull request template to encourage the creation of client pull requests before breaking changes are merged.

References

Changelog

Checklist

• [x] I've updated the test suite for new or updated code as appropriate
• [x] I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• [x] I've highlighted breaking changes using the "BREAKING" category above as appropriate