feat: add typings and interfaces for Overlay Specification v1.0.0

* updated references to use defined NodeTypes.
* update `any` to `unknown`

related #1246

.changeset/stale-starfishes-rule.md

@@ -0,0 +1,6 @@
+---
+"@redocly/openapi-core": minor
+"@redocly/cli": minor
+---
+
+Add typings and interfaces for Overlay Specification v1.0.0

packages/core/src/types/overlay.ts

@@ -0,0 +1,46 @@
+import { type NodeType, type NormalizedScalarSchema, listOf } from '.';
+
+const Root: NodeType = {
+  properties: {
+    overlay: { type: 'string' },
+    info: 'Info',
+    extends: 'Extends',
+    actions: 'Actions'
+  },
+  required: ['overlay', 'info', 'actions'],
+  extensionsPrefix: 'x-',
+};
+
+const Info: NodeType = {
+  properties: {
+    title: { type: 'string' },
+    version: { type: 'string' },
+  },
+  required: ['title', 'version'],
+  extensionsPrefix: 'x-',
+};
+
+const Extends: NormalizedScalarSchema = {
+  type: 'string',
+  resolvable: true,
+};
+
+const Actions: NodeType = listOf('Action');
+const Action: NodeType = {
+  properties: {
+    target: { type: 'string' },
+    description: { type: 'string' },
+    update: {}, // any
+    remove: { type: 'boolean' },
+  },
+  required: ['target'],
+  extensionsPrefix: 'x-',
+};
+
+export const OverlayTypes: Record<string, NodeType | NormalizedScalarSchema> = {
+  Root,
+  Info,
+  Extends,
+  Actions,
+  Action,
+};

packages/core/src/typings/overlay.ts

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+export interface InfoObject {
+  title: string;
+  version: string;
+}
+
+export interface ActionObject {
+  target: string;
+  description?: string;
+  update?: unknown;
+  remove?: boolean;
+}
+export interface OverlayDefinition {
+  overlay: '1.0.0';
+  info: InfoObject;
+  extends?: string;
+  actions: ActionObject[];
+}
+
+export const VERSION_PATTERN = /^1\.0\.\d+(-.+)?$/;