docker.#Push: Set auth as optional

Signed-off-by: Guillaume de Rouville <guillaume.derouville@gmail.com>

docs/reference/universe/docker/README.md

@@ -78,8 +78,6 @@ Push a docker image to a remote registry
 | -------------    |:-------------:        |:-------------:                                             |
 |*target*          | `string`              |Remote target (example: "index.docker.io/alpine:latest")    |
 |*source*          | `dagger.#Artifact`    |Image source                                                |
-|*auth.username*    | `string`              |Username                                                    |
-|*auth.secret*      | `string`              |Password or secret                                          |
 
 ### docker.#Push Outputs
 

stdlib/docker/docker.cue

@@ -37,7 +37,7 @@ import (
 	source: dagger.#Artifact @dagger(input)
 
 	// Registry auth
-	auth: {
+	auth?: {
 		// Username
 		username: string @dagger(input)