fix: use container-local config dir path when reading arguments

[BilliAlpha]

Fixes #235

The letsencrypt_configure_and_get_dir function now returns both the host and container path to the config_dir separated by a colon (:).

In subcommands, functions calling letsencrypt_configure_and_get_dir now parse the returned paths to split by colon and populate two variables: host_config_dir and container_config_dir.