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
As suggested in review: The `GITHUB_REPOSITORY` environment variable is
only available on Actions. Passing it in explicitly avoids potentially
crashing if this code is called from the runner.