Dynamic configuration

[kristofferlind]

Configuration changes

• outputs are now a dynamic list instead of 2 hardcoded entries
• actions are now set through configuration instead of a hardcoded set of available actions

Development tooling:

• test setup with bats, testing actual usage
• test and release workflows
• prepared environment for development, with direnv and nix installed everything is ready when entering directory

Security improvements:

• a massive reduction of dependencies
• no longer expects any credentials to be set (login to registries/repositories is now expected to be done prior to execution instead)