Adding schema definitions endpoint

Introduces new schema definitions endpoint, allowing the caller to get
the fields/types/descriptions for a given kubernetes resource.

pkg/schema/definitions/schema.go

@@ -0,0 +1,51 @@
+package definitions
+
+import (
+	"time"
+
+	"github.com/rancher/apiserver/pkg/types"
+	"github.com/rancher/wrangler/v2/pkg/schemas"
+	"k8s.io/client-go/discovery"
+)
+
+const (
+	gvkExtensionName    = "x-kubernetes-group-version-kind"
+	gvkExtensionGroup   = "group"
+	gvkExtensionVersion = "version"
+	gvkExtensionKind    = "kind"
+	defaultDuration     = time.Second * 5
+)
+
+// Register registers the schemaDefinition schema.
+func Register(baseSchema *types.APISchemas, client discovery.DiscoveryInterface) {
+	handler := schemaDefinitionHandler{
+		client:       client,
+		refreshStale: defaultDuration,
+	}
+	baseSchema.MustAddSchema(types.APISchema{
+		Schema: &schemas.Schema{
+			ID:              "schemaDefinition",
+			PluralName:      "schemaDefinitions",
+			ResourceMethods: []string{"GET"},
+		},
+		ByIDHandler: handler.byIDHandler,
+	})
+}
+
+type schemaDefinition struct {
+	DefinitionType string                `json:"definitionType"`
+	Definitions    map[string]definition `json:"definitions"`
+}
+
+type definition struct {
+	ResourceFields map[string]definitionField `json:"resourceFields"`
+	Type           string                     `json:"type"`
+	Description    string                     `json:"description"`
+}
+
+type definitionField struct {
+	Type        string `json:"type"`
+	SubType     string `json:"subtype,omitempty"`
+	Description string `json:"description,omitempty"`
+	Required    bool   `json:"required,omitempty"`
+}