Fix failing RPM builds due to files ignored by Git

[apyrgio]

Fix failing RPM builds by doing the following:

1. Remove .gitignore from a dir where Poetry would ultimately build our Python wheel.
2. Include data files only on sdist, and in a way that Poetry understands.

Fixes #678
Refs #677

[deeplow]

On another discussion you also mentioned:

Turns out that Poetry will silently ignore everything and create an empty wheel, without any indication in the logs. If you don't have git installed, or do this from any other path in your system, Poetry will create a functional wheel. See python-poetry/poetry#2809.

Do you want to add an assert that git exists? It'll be kind of an edge-case but might be worth referencing somewhere since you came across it.

[apyrgio]

We can't assert that Git exists, because it's not a requirement for build our RPM packages. Actually, some of our CI runners don't have Git installed, which is why we could build RPM packages all this time.

[deeplow]

LGTM. I tried installing and running and it worked well.

I also uncompressed the .rpm file with rpm2cpio dangerzone*.rpm | cpio -idmv and confirmed the files made sense. It even put the README.md in the doc directory and didn't include anything in the install/.

I have tested on any other platforms but since you concluded that PEP-517 isn't really used by other platforms for building, I don't expect any of that to break.