[FEATURE REQUEST] Auto-format pull requests

[Pante]

Is your feature request related to a problem? Please describe.
Our code convention differs from most other projects. There will be less burden on both the reviewer and reviewee's sides if the code is automatically formatted before review.

Describe the solution you'd like
Set-up https://github.com/diffplug/spotless/tree/main/plugin-maven#java or some other auto-formatting tool as part of the project's CI/CD.

Describe alternatives you've considered
Continue manually formatting pull requests which generates more churn.