initial Fastlane structures from IzzyOnDroid

this PR provides you with a "fastlane starter package". Some notes to sum them up in a place easy to find for you: * the [IzzyOnDroid Fastlane Documentation](https://gitlab.com/IzzyOnDroid/repo/-/wikis/Fastlane) can guide you with maintaining the structures here * take special care for limits, e.g. per-release changelogs can have max 500 chars, `full_description.txt` max 4,000 chars, graphics must have specific aspect ratios etc. * you can have "bigger graphics" here; the IoD updater takes care to resize/optimize them as needed * for the `full_description.txt` here I've used HTML compressed into a single line, to prevent the fdroid software converting each line break to a `<br>`. The tags used for this are supported by F-Droid.org as well, and to my knowledge even by PlayStore. * Details on all this in the linked documentation. * Should you have questions, be welcome to ask :wink: And now: Enjoy!