fix(schema): use enum for secret pull policy (#331)

yaml/secret.go

@@ -25,7 +25,7 @@ type (
 		Engine string `yaml:"engine,omitempty" json:"engine,omitempty" jsonschema:"enum=native,enum=vault,default=native,description=Name of storage backend to fetch secret from.\nReference: https://go-vela.github.io/docs/reference/yaml/secrets/#the-engine-tag"`
 		Type   string `yaml:"type,omitempty"   json:"type,omitempty" jsonschema:"enum=repo,enum=org,enum=shared,default=repo,description=Type of secret to fetch from storage backend.\nReference: https://go-vela.github.io/docs/reference/yaml/secrets/#the-type-tag"`
 		Origin Origin `yaml:"origin,omitempty" json:"origin,omitempty" jsonschema:"description=Declaration to pull secrets from non-internal secret providers.\nReference: https://go-vela.github.io/docs/reference/yaml/secrets/#the-origin-tag"`
-		Pull   string `yaml:"pull,omitempty"   json:"pull,omitempty" jsonschema:"default=build_start,description=When to pull in secrets from storage backend."`
+		Pull   string `yaml:"pull,omitempty"   json:"pull,omitempty" jsonschema:"enum=step_start,enum=build_start,default=build_start,description=When to pull in secrets from storage backend.\nReference: https://go-vela.github.io/docs/reference/yaml/secrets/#the-pull-tag"`
 	}
 
 	// Origin is the yaml representation of a method