ability to export all secrets as an encrypted json document

[v0lkan]

User will provide their public key; aegis-sentinel will encrypt things and export them.

note that same api can be used to read the value of a key: give me a public key; get an encrypted secret value.

by design sentinel will NEVER expose plain text secrets to operators.

[v0lkan]

• We can use age encryption keys here too, to keep things consistent.
• We can also make a tool (that wraps around age) to make encryption and key generation easier
• or we can make that functionality part of sentinel.