refactor: compose deployment with pluggable spec resolver, basic test

internal/cli/client/operation.go

@@ -11,6 +11,9 @@ import (
 // Operation represents a single atomic operation in a deployment process.
 // Operations can be composed to form complex deployment strategies.
 type Operation interface {
+	// Execute performs the operation using the provided client.
+	// TODO: Encapsulate the client in the operation as otherwise it gives an impression that different clients
+	//  can be provided. But in reality, the operation is tightly coupled with the client that was used to create it.
 	Execute(ctx context.Context, cli *Client) error
 	// Format returns a human-readable representation of the operation.
 	Format(resolver NameResolver) string