refactor: bcrypt key derivation to aead (#509)

[bizk]

• Added Aead encryption and Argon2 key derivation to armor## Description

Closes: #3129

• Replaced bcrypt key derivation for argon2id, this approach is secure and resolves most of bcrypt common issues. Algorithm implementation uses these parameters

const (
	argon2Time    = 1 // Recommended by library authors: Uses max memory available
	argon2Memory  = 64 * 1024 // Memory usage 
	argon2Threads = 4
	argon2KeyLen  = 32 // Key bytes
)

• Replaced xsalsa20 symmetric encryption with AEAD ChaCha20Poly
• Added backward compatibility for old keys.
• Added respective tests
• Fixed suggestions and comments by @facundomedica
• fix different lint errors
• Fixed comments, and added error handling messages
• added error default value for kdf switch case and error handling
• added missing error message for unarmor when having a bad passphrase

---

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[facundomedica]

LGTM, would love a quick review from @FiloSottile 🙏

[FiloSottile]

LGTM

[FiloSottile]

Probably worth a comment explaining that it's ok to use a fixed (all zeroes) nonce because the key is generated fresh at every encryption using a fresh random salt every time. If nothing else because it's very important that the code is not changed later to reuse the same salt and passphrase with different private keys.

(By the way, the salt is 128 bits, which gives a 2^-32 chance of collision after 2^50 encryptions. Is that a particularly realistic concern? No. Is it worth making the salt 24 bytes if it's just a matter of changing a constant? Probably.)

[facundomedica]

@bizk let's address Filippo's comments and merge it 👌

[bizk]

Hi solved the comments @FiloSottile also thanks @facundomedica for following up :)

[tac0turtle]

@bizk could you fix the linting issue then the bot will merge the pr