contrib/emacs: adding a variable for file extensions

[Nicolas Graves]

Hi!

I was trying to use the fork of password-store named passage (using
encryption with age instead of gpg), and setup an emacs config for it.

Since the fork stays quite close to the original password-store, changes
that need to be made are actually quite small, and mainly concern
changes related to "gpg" strings that need to be replaced by "age"
strings.

Would it be possible to add a defvar or a defcustom variable with this
string, to be able to use the same emacs package instead of forking it ?
Would a patch implementing this change for contrib/emacs be merged (I
was thinking about a variable password-store-file-extension) ?

-- 
Best regards,
Nicolas Graves