Add Save Contact info (as VCF or JSON) - Feature request

Related to https://github.com/gzuuus/linktr-nostr/issues/20

Useful to import the contact info in the user Contacts on their devices.

VCF - Vcard example:

BEGIN:VCARD
VERSION:3.0
N:Coen;David ;
EMAIL;TYPE=work:info@davidcoen.it
TEL;TYPE=work:39....
URL;TYPE=linktree:https://linktr.ee/thedavidcoen
END:VCARD