easier 'diff'

[raboof]

It would be nice to be able to more easily 'diff' secrets between git commits.

textconv gets us part of the way there: if you add a .gitattributes with *.age diff=age and then edit .git/config to:

[diff "age"]
        textconv = age -d -i ~/.ssh/id_ed25519

... this sorta seems to work, except in my case ~/.ssh/id_ed25519 is password-protected, and it seems the pager interferes with my password entry.

Upstream age is not a fan of encrypted keys in the first place (https://github.com/FiloSottile/age/issues/366#issuecomment-981610446)

If this worked more smoothly it might be worth documenting it and perhaps providing an 'agenix wrapper', but for now I'll just leave my learnings here ;)