Add gitignore and automatic code formatting

[lfoppiano]

Hi all,
I did some cleanups and added the Spotless pluging with the CI.
I noticed there was a class with weird / missing indentation and that the .gitignore was missing so I took the opportunity to do so.
Now the CI will fail enforcing formatting. This would work well if we squash/merge and disable the commits directly on main.

Note: I did use a spotless configuration more of my preference, but I have not problems to adapt that to what maintainers require.

[sebastian-nagel]

Thanks, @lfoppiano. Looks good.

However, a principal question is whether we shouldn't instead follow the upstream code formatting rules? StormCrawler uses the Cosium formatter and Git pre-commit hooks, see the Note for Developers in the README. Using the same formatting rules might help to keep the code in sync. Some classes in news crawler are borrowed from StormCrawler.

[lfoppiano]

@sebastian-nagel good point. I've removed spotless and implemented Cosium. It's worth the effort to match the storm-crawler now so that we won't have problems with code diffs.

[sebastian-nagel]

Thanks, @lfoppiano. Looks good, except for the license headers - see the inline comment.

+1 to stash and merge once the headers are fixed.