Comment 0 for bug 1763839

As discussed previously, we want to have zstd support in 16.04 to evaluate and potentially enable it in later releases. We also want to add hooks for snap integration to apt, this release is supposed to add them to.

The concrete code is still undergoing review, some option names might change for the hooks before release (e.g. pre-download might become pre-install-prompt, and the AptCli::Hooks config section only gets Install and Search lists for hooks to register, rather than individual pre-, post-, and fail- lists).

The attached patch is thus preliminary but should be fairly identical to the final result.