Create public encrypt pkg and references to it

[manute]

Creates the encrypt pkg and refactorize the code to change all the references to it

[nachtjasmin]

Unfortunately, the given package interface is pretty rudimentary and requires a lot of manual plumbing by callers to work with the stores and all that. In comparison, the decrypt package provides much more integration and doesn't require callers to duplicate current behaviour from the current CLI. :/

I tried to integrate it but stopped after I realised that I'd duplicate the CLI at several points.

[manute]

@nachtjasmin yeah I noticed that, thanks for the feedback. This PR it is only to have it as public interface to not have to duplicate the file - so with the pkg of this PR you can implement a method like :

func EncryptWith(awsKmsArn, filePath string) ([]byte, error) {

	masterKey := kms.MasterKey{
		Arn: awsKmsArn,
	}

	opts := encrypt.EncryptOpts{
		Cipher: aes.NewCipher(),
		KeyServices: []keyservice.KeyServiceClient{
			keyservice.NewLocalClient(),
		},
		InputStore:  &yaml.Store{},
		OutputStore: &yaml.Store{},
		InputPath:   filePath,
		EncryptConfig: encrypt.EncryptConfig{
			KeyGroups: []sops.KeyGroup{
				[]keys.MasterKey{&masterKey},
			},
		},
	}

	return encrypt.Encrypt(opts)
}

so at least you have more control over it 👍🏽