Unifi CLI of backup and restic modules of k8up

[cimnine]

Summary

As user of k8up
I want a stringent usage of the tool
So that I can reduce learning to a minimum.

Context

#359 moved the wrestic code into the k8up repository, but did try to changes as little as possible of the architecture.
The idea of this issue is to unify the command line interface of the two modules, operator and restic.

Currently, the two modules have different concepts to deal with arguments and variables. While the operator module is mostly relying on environment variables, the restic module mostly relies on command line arguments.

One unified approach could be that for every argument, both are possible: CLI argument and environment variable.

Out of Scope

• Changes to the functionality.

Further links

• Move wrestic into the K8up repository #359

Acceptance criteria

• Given k8up help, when looking through the available commands and arguments, the two modules seem to have been developed with the same usage concepts in mind.

Implementation Ideas

The cli library in use already supports environment variables for CLI arguments. This could be leveraged to unifi the command line interface of the two modules.

If this change is not backwards compatible, make sure to adjust the relevant documentation, code parts, configuration examples, default configuration values, etc.