* Remove `let` from the script as it will return 1 (signalling an error) on the
first iteration, which will stop the script when in `set -e` mode.
It also is unnecessary, as the increment can be done at the place of
usage directly.
* Added a "remainder aka modulo" division, otherwise there will be no
TLP option set, once we run out of the four entries in the TLSs
list.
* (Style) remove superfluous semicolons.
* Add an OpenPGP test keypair.
* Move script parts of documentation into script, so they can be used on a fresh Ubuntu 20.04 system
for within a github action to setup a csaf_provider and upload documents to it for an integration test.
* Use dineshsonachalam/markdown-autodocs in github action to automatically
insert lines from the scripts into the docs.
Co-authored-by: Bernhard Reiter <bernhard@intevation.de>