[Feature Request] Symmetric config encryption with password

I'm not sure if this is something that the SOPS team is interested in, but I've been meaning to write up a simple library to do symmetric encryption with a password for config files in Golang.

So it looks something like this:

sops --encrypt --password test.yaml > test.enc.yaml
Enter your password: 
Verify password:

Something similar to the code in https://github.com/isfonzar/filecrypt, using GCM and the Golang "golang.org/x/crypto/pbkdf2" library:

	key := password
	nonce := make([]byte, 12)

	// Randomizing the nonce
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		panic(err.Error())
	}

	dk := pbkdf2.Key(key, nonce, 4096, 32, sha1.New)

	block, err := aes.NewCipher(dk)
	if err != nil {
		panic(err.Error())
	}

	aesgcm, err := cipher.NewGCM(block)
	if err != nil {
		panic(err.Error())
	}

	ciphertext := aesgcm.Seal(nil, nonce, plaintext, nil)

Start by reviewing SOPS's existing encryption command flow and the referenced filecrypt implementation; the issue names no repository files or tests. Clarify the password prompt, key derivation, authenticated encryption, file format, and compatibility requirements before defining what a complete implementation and its tests would cover.