fix: in the image-spec validations and docs (#2302)

## Description
fix: in the image-spec validations and docs

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## Is this change user facing?
YES

## References (if applicable)
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core/server/api_container/server/startosis_engine/kurtosis_types/service_config/image_spec.go

@@ -53,7 +53,7 @@ func NewImageSpec() *kurtosis_type_constructor.KurtosisTypeConstructor {
 					IsOptional:        true,
 					ZeroValueProvider: builtin_argument.ZeroValueProvider[starlark.String],
 					Validator: func(value starlark.Value) *startosis_errors.InterpretationError {
-						return builtin_argument.NonEmptyString(value, ImageRegistryUsernameAttr)
+						return builtin_argument.NonEmptyString(value, ImageRegistryPasswordAttr)
 					},
 				},
 			},

docs/docs/api-reference/starlark-reference/service-config.md

@@ -23,7 +23,7 @@ config = ServiceConfig(
     image = ImageSpec(
         #  The name of the image that needs to be pulled qualified with the registry
         # MANDATORY
-        name = "my.registry.io/my-user/my-image",
+        image = "my.registry.io/my-user/my-image",
 
         # The username that will be used to pull the image from the given registry
         # OPTIONAL