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/init-action.ts

@@ -148,6 +148,7 @@ async function run() {
     externalRepoAuth: getOptionalInput("external-repository-token"),
     url: getRequiredEnvParam("GITHUB_SERVER_URL"),
     apiURL: getRequiredEnvParam("GITHUB_API_URL"),
+    registriesAuthTokens: getOptionalInput("registries-auth-tokens"),
   };
 
   const gitHubVersion = await getGitHubVersionActionsOnly();