Automate list of languages for which to create localised screenshots

The list of languages to consider for screenshot creation is currently manually identified: https://github.com/AntennaPod/StoreMetadata/blob/32234b716df30aaaa8a2d08e3ac4dad5e795bc7e/screenshots/01_takeScreenshots.sh#L116

It'd be better to automate that, so we don't have to think about keeping the langue list up to date. Two approaches:
* Create a separate language list file under `/StoreMetadata/screenshots`, which we update with GH workflows (in the app repo or in this repo, depending on the criteria we decide on)
* Let the script check an external/existing file or folder (again, depending on the criteria we decide on)

Then we also need to decide what our criterium is:
* we release the app in that language, i.e. we can make localised screenshots (https://github.com/AntennaPod/AntennaPod/blob/develop/.tx/config)
* we have the screenshot title strings in that language, i.e. we can make localised frames (`/screenshots/strings/...`)
* both of the above: we have screenshot titles in that language _and_ release the app in that language.

To have the widest possible set of screenshots, I would go for the first option.

@ByteHamster Would you agree with me on the criteria for `01_takeScreenshots.sh`? And for the approach, do you have a preference?

When we have a decision on both points I'd be happy to start tinkering and prepare a PR.

---

Also for the final play store images, the list of languages is defined manually: https://github.com/AntennaPod/StoreMetadata/blob/32234b716df30aaaa8a2d08e3ac4dad5e795bc7e/screenshots/02_frameScreenshots.py#L8

We'll want to automate that language list one as well, and need a similar decision on criteria. For me, having a localised play store image title with an English screenshot gives a bit of an odd signal to the user: we want to promote in your language but we don't care enough to translate the actual app. So this I would avoid.

So here we should, I think, consider a combination of both criteria.