(core) Adding latest version section to the admin panel.

Summary:
Update for the admin page to show the latest available version information.
- Latest version is read from docs.getgrist.com by default
- It sends basic information (installationId, deployment type, and version)
- Checks are done only on the page itself
- The actual request is routed through the API (to avoid CORS)

Test Plan: Added new test

Reviewers: paulfitz

Reviewed By: paulfitz

Subscribers: paulfitz

Differential Revision: https://phab.getgrist.com/D4238

app/common/InstallAPI.ts

@@ -24,9 +24,38 @@ export interface PrefWithSource<T> {
 
 export type PrefSource = 'environment-variable' | 'preferences';
 
+
+/**
+ * JSON returned to the client (exported for tests).
+ */
+export interface LatestVersion {
+  /**
+   * Latest version of core component of the client.
+   */
+  latestVersion: string;
+  /**
+   * If there were any critical updates after client's version. Undefined if
+   * we don't know client version or couldn't figure this out for some other reason.
+   */
+  isCritical?: boolean;
+  /**
+   * Url where the client can download the latest version (if applicable)
+   */
+  updateURL?: string;
+
+  /**
+   * When the latest version was updated (in ISO format).
+   */
+  updatedAt?: string;
+}
+
 export interface InstallAPI {
   getInstallPrefs(): Promise<InstallPrefsWithSources>;
   updateInstallPrefs(prefs: Partial<InstallPrefs>): Promise<void>;
+  /**
+   * Returns information about latest version of Grist
+   */
+  checkUpdates(): Promise<LatestVersion>;
 }
 
 export class InstallAPIImpl extends BaseAPI implements InstallAPI {
@@ -45,6 +74,10 @@ export class InstallAPIImpl extends BaseAPI implements InstallAPI {
     });
   }
 
+  public checkUpdates(): Promise<LatestVersion> {
+    return this.requestJson(`${this._url}/api/install/updates`, {method: 'GET'});
+  }
+
   private get _url(): string {
     return addCurrentOrgToPath(this._homeUrl);
   }

app/common/gristUrls.ts

@@ -105,6 +105,8 @@ export const commonUrls = {
   gristLabsWidgetRepository: 'https://github.com/gristlabs/grist-widget/releases/download/latest/manifest.json',
   githubGristCore: 'https://github.com/gristlabs/grist-core',
   githubSponsorGristLabs: 'https://github.com/sponsors/gristlabs',
+
+  versionCheck: 'https://api.getgrist.com/api/version',
 };
 
 /**