Support --armor

[fzakaria]

I like commiting non-binary data and age supports --armor to generate a PEM style;e base64 file.
I think the secrets.nix file should/could support this as an argument when generate the age secrets.

[dlubawy]

This is certainly doable. I added it in on a dirty branch containing other fixes for my personal use. The commit adds the attribute armor to be set within secrets.nix, and then it checks if the attribute is true/false which determines whether to add --armor to the age bin call.

It should be easy to pull that out into a clean branch that could be merged into main.

[fzakaria]

Contribute it :)