adapt slkspec to new HSM proxy

[neumannd]

• switched to new hsm package and recall/HSM proxy for starting and organizing recalls
• considerably simplified code basis in the context of switching to the HSM proxy

This is for release 0.1.0 or similar. This PR contains breaking changes. It requires a package hsm which is still undergoing a test phase at DKRZ.

[neumannd]

Leave it this way until hsm package is made available. It is also not included in the pyproject.toml yet.