This input is exposed in the CodeQL CLI as the flag --source-root, allowing
users of the CLI to set --source-root different from --working-dir. However,
in codeql-action, these two paths are conflated and it poses problems for
users with complicated build environments, in which a source root may be
a child of the working directory.
Most users should not notice this, as the default value is
${{ github.workspace }}, as it is implied now (`path.resolve()`).
This input allows users to specify which packs to run. It works in
unison with the packs block of the config file and it is similar to
how `queries` works. They both use `+` in the same way.
Note that the `#TODO` in the pr check is still around, but the CLI
is available. I will remove the TODO in the next commit.
