Add possibility for user to provide setup and cleanup scripts for
additional flexibility. Setup-script takes precedence over the built-in
behavior of uacme.

This helps users with more complex use-cases to utilize uacme to update
certificates without adding complexity to the provided run.sh script.

Signed-off-by: Antti Seppälä <a.seppala@gmail.com>

lightweight client for the RFC8555 ACMEv2 protocol, written in plain C code
with minimal dependencies (libcurl and one of GnuTLS, OpenSSL or mbedTLS).

Signed-off-by: Lucian Cristian <lucian.cristian@gmail.com>