Handle secrets in DockerLogin operation

Before, secret was a plain text string, but it could lead to security issue
so we are now handling secrets as `dagger.#Secret` or string.
I've add a new struct SecretStore that expose the inputStore to easily
retrieve secret value.

Signed-off-by: Tom Chauveau <tom.chauveau@epitech.eu>

stdlib/dagger/op/op.cue

@@ -68,7 +68,7 @@ package op
 	target:   string
 	username: string
 	// FIXME: should be a #Secret (circular import)
-	secret: string | bytes
+	secret: _ @dagger(secret)
 }
 
 #FetchContainer: {