Add support for downloading packs from GHES

This change adds:

- new `registries` block allowed in code scanning config file
- new `registries-auth-tokens` input in init action
- Change the downloadPacks function so that it accepts new parameters:
    - registries block
    - api auth
- Generate a qlconfig.yml file with the registries block if one is
  supplied. Use this file when downloading packs.
- temporarily set the `GITHUB_TOKEN` and `CODEQL_REGISTRIES_AUTH` based
  on api auth

TODO:

1. integration test
2. handle pack downloads when the config is generated by the CLI

src/api-client.ts

@@ -4,7 +4,7 @@ import * as githubUtils from "@actions/github/lib/utils";
 import * as retry from "@octokit/plugin-retry";
 import consoleLogLevel from "console-log-level";
 
-import { getRequiredInput } from "./actions-util";
+import { getOptionalInput, getRequiredInput } from "./actions-util";
 import * as util from "./util";
 import { getMode, getRequiredEnvParam, GitHubVersion } from "./util";
 
@@ -23,6 +23,7 @@ export interface GitHubApiDetails {
   auth: string;
   url: string;
   apiURL: string | undefined;
+  registriesAuthTokens: string | undefined;
 }
 
 export interface GitHubApiExternalRepoDetails {
@@ -68,6 +69,9 @@ function getApiDetails() {
     auth: getRequiredInput("token"),
     url: getRequiredEnvParam("GITHUB_SERVER_URL"),
     apiURL: getRequiredEnvParam("GITHUB_API_URL"),
+
+    // only available in the init action
+    registriesAuthTokens: getOptionalInput("registries-auth-tokens"),
   };
 }