Allow to use a Github Auth token for fetching releases

This change allows to use a authorization token provided by Github in
order to fetch metadata for a RA release. Using an authorization token
prevents to get rate-limited in environments where lots of RA users use
a shared client IP (e.g. behind a company NAT).

The auth token is stored in `ExtensionContext.globalState`.
As far as I could observe through testing with a local WSL2 environment
that state is synced between an extension installed locally and a remote
version.

The change provides no explicit command to query for an auth token.
However in case a download fails it will provide a retry option as well
as an option to enter the auth token. This should be more discoverable
for most users.

Closes #3688

editors/code/src/persistent_state.ts

@@ -38,4 +38,15 @@ export class PersistentState {
     async updateServerVersion(value: string | undefined) {
         await this.globalState.update("serverVersion", value);
     }
+
+    /**
+     * Github authorization token.
+     * This is used for API requests against the Github API.
+     */
+    get githubToken(): string | undefined {
+        return this.globalState.get("githubToken");
+    }
+    async updateGithubToken(value: string | undefined) {
+        await this.globalState.update("githubToken", value);
+    }
 }