Add separate subcommands for encryption, decryption, rotating, editing, and setting values

[felixfontein]

This is a Work in Progress for exploring how to implement #1333. Right now the new subcommands are basically a stripped-down copy'n'paste of the current "main" command.

Fixes #1333

[felixfontein]

I saw that you tried to remove duplicated flags. Here are a few remaining ones if you want.

My goal with this PR for now is to check out how creating subcommands could work. There are quite a few PRs waiting to get processed that add a lot of rebase work to this one, so I might also just ditch it and re-start from scratch.

Thanks for marking the other ones, I'll take a look at them at some point once this is more stable...

[duthils]

@felixfontein can this PR be closed, now that #1391 is merged?

[felixfontein]

This is mainly still open for the flag de-duplication. I wanted to continue working on this once some more PRs are merged, which unfortunately never happened until now.