feat: move tui code to tui package

[brianmcgee]

It makes PluginTerminalUI available for sops (and other third parties) to support plugins more easily.

[felixfontein]

From the SOPS point of view, having this as a reusable package would be really great! Basically copy'n'pasting that code over (and keeping it up-to-date) would IMO be a last-resort solution, which I'd like to avoid.

[Mic92]

CI needs a fix:

Error: cmd/age-keygen/keygen.go:161:13: non-constant format string in call to log.Printf

[brianmcgee]

I missed that the static checks needed to be fixed. I just cherry-picked #589 into this branch.

@FiloSottile, it would be great if we could get this merged 🙏

[Mic92]

Friendly ping

[Mic92]

I guess a long-term fork, it is than. Someone else interested in maintaining it? We could create some org that contains both age and sops with this feature. We would probably just need to merge with upstream every once in a while.

[felixfontein]

@FiloSottile any kind of feedback (like whether this has a chance of eventually getting merged) would be great!

[visualphoenix]

+1 would be great to have this merged

[NovaViper]

@brianmcgee hey looks like #589 just got merged!