Hash and encrypt connection data

[Le0Developer]

Describe the feature

Currently we have plaintext connection data (eg email, discord id, patreon id, github id). Not good.

We don't need to know the actual value, just if there is a match, so we can safely hash it. However then the user doesn't know what email they linked in their overview, so we should aloso encrypt the connection data with the user's public key, so it can be decrypted locally.

Use case

Increased privacy and robustness against DB compromise.

Additional context

No response

[Le0Developer]

Just realized we cant do this for Discord, since #58 is using the discord ids to ping for updates.