Add Open VSX default and an env var for marketplace, fix old marketplace

Our old marketplace only supports `serviceUrl` but this causes the marketplace
to be disabled entirely so this moves the template var check to fix that.

This can be tested by setting EXTENSIONS_GALLERY set to:

    '{"serviceUrl": "https://extensions.coder.com/api"}'


Index: code-server/lib/vscode/src/vs/platform/product/common/product.ts
===================================================================
--- code-server.orig/lib/vscode/src/vs/platform/product/common/product.ts
+++ code-server/lib/vscode/src/vs/platform/product/common/product.ts
@@ -45,7 +45,14 @@ else if (typeof require?.__$__nodeRequir
 	}
 
 	Object.assign(product, {
-		version: pkg.version
+		version: pkg.version,
+		extensionsGallery: env.EXTENSIONS_GALLERY ? JSON.parse(env.EXTENSIONS_GALLERY) : (product.extensionsGallery || {
+			serviceUrl: "https://open-vsx.org/vscode/gallery",
+			itemUrl: "https://open-vsx.org/vscode/item",
+			resourceUrlTemplate: "https://open-vsx.org/vscode/asset/{publisher}/{name}/{version}/Microsoft.VisualStudio.Code.WebResources/{path}",
+			controlUrl: "",
+			recommendationsUrl: "",
+		}),
 	});
 }
 
Index: code-server/lib/vscode/src/vs/server/node/webClientServer.ts
===================================================================
--- code-server.orig/lib/vscode/src/vs/server/node/webClientServer.ts
+++ code-server/lib/vscode/src/vs/server/node/webClientServer.ts
@@ -293,14 +293,14 @@ export class WebClientServer {
 					rootEndpoint: base,
 					codeServerVersion: this._productService.codeServerVersion,
 					embedderIdentifier: 'server-distro',
-					extensionsGallery: this._webExtensionResourceUrlTemplate ? {
+					extensionsGallery: {
 						...this._productService.extensionsGallery,
-						'resourceUrlTemplate': this._webExtensionResourceUrlTemplate.with({
+						'resourceUrlTemplate': this._webExtensionResourceUrlTemplate ? this._webExtensionResourceUrlTemplate.with({
 							scheme: 'http',
 							authority: remoteAuthority,
 							path: `web-extension-resource/${this._webExtensionResourceUrlTemplate.authority}${this._webExtensionResourceUrlTemplate.path}`
-						}).toString(true)
-					} : undefined
+						}).toString(true) : undefined
+					},
 				}
 			})))
 			.replace('{{WORKBENCH_AUTH_SESSION}}', () => authSessionInfo ? escapeAttribute(JSON.stringify(authSessionInfo)) : '')