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

lib/feature-flags.test.js

@@ -17,6 +17,7 @@ const testApiDetails = {
     auth: "1234",
     url: "https://github.com",
     apiURL: undefined,
+    registriesAuthTokens: undefined,
 };
 const testRepositoryNwo = (0, repository_1.parseRepositoryNwo)("github/example");
 const ALL_FEATURE_FLAGS_DISABLED_VARIANTS = [