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/util.test.ts

@@ -209,6 +209,7 @@ test("getGitHubVersion", async (t) => {
     auth: "",
     url: "https://github.com",
     apiURL: undefined,
+    registriesAuthTokens: undefined,
   });
   t.deepEqual(util.GitHubVariant.DOTCOM, v.type);
 
@@ -217,6 +218,7 @@ test("getGitHubVersion", async (t) => {
     auth: "",
     url: "https://ghe.example.com",
     apiURL: undefined,
+    registriesAuthTokens: undefined,
   });
   t.deepEqual(
     { type: util.GitHubVariant.GHES, version: "2.0" } as util.GitHubVersion,
@@ -228,6 +230,7 @@ test("getGitHubVersion", async (t) => {
     auth: "",
     url: "https://example.githubenterprise.com",
     apiURL: undefined,
+    registriesAuthTokens: undefined,
   });
   t.deepEqual({ type: util.GitHubVariant.GHAE }, ghae);
 
@@ -236,6 +239,7 @@ test("getGitHubVersion", async (t) => {
     auth: "",
     url: "https://ghe.example.com",
     apiURL: undefined,
+    registriesAuthTokens: undefined,
   });
   t.deepEqual({ type: util.GitHubVariant.DOTCOM }, v3);
 });