feat: add User-Agent header to HTTP/HTTPS schema fetch requests

Include a well-formed RFC 9110-compliant User-Agent on all direct xhr calls
when fetching schemas over HTTP or HTTPS:

  yaml-language-server/<version> (RedHat) node/<nodeVersion> (<platform>)

The server version is read from YAML_LANGUAGE_SERVER_VERSION, the Node.js
version from process.versions.node, and the platform from process.platform.
All three are guarded with typeof-process checks for browser/web worker
safety, falling back to 'unknown' for the version and omitting the runtime
and platform tokens entirely in non-Node environments.

Author: svifred

src/languageservice/services/schemaRequestHandler.ts

@@ -88,7 +88,13 @@ export const schemaRequestHandler = async (
     }
 
     // Send the HTTP(S) schema content request and return the result
-    const headers = { 'Accept-Encoding': 'gzip, deflate' };
+    const version = (typeof process !== 'undefined' && process.env.YAML_LANGUAGE_SERVER_VERSION) || 'unknown';
+    const nodeVersion = typeof process !== 'undefined' && process.versions?.node ? ` node/${process.versions.node}` : '';
+    const platform = typeof process !== 'undefined' && process.platform ? ` (${process.platform})` : '';
+    const headers = {
+      'Accept-Encoding': 'gzip, deflate',
+      'User-Agent': `yaml-language-server/${version} (RedHat)${nodeVersion}${platform}`,
+    };
     return xhr({ url: uri, followRedirects: 5, headers }).then(
       (response) => {
         return response.responseText;