Add the ability for the CLI SSL security commands to be able to obtain a server certificate from Let's Encrypt

WFCORE-3447 introduced high-level security commands (ssl enable-ssl-management and ssl enable-ssl-http-server) for enabling one-way and two-way SSL easily. To generate the server certificate, these high-level security commands made use of key-store management operations to generate a self-signed certificate. Since it is now possible to obtain certificates from the Let's Encrypt certificate authority using the CLI, the high-level security commands should be updated so that in addition to being able to generate a self-signed server certificate, they can also obtain a server certificate from Let's Encrypt. Details on the new management operations for obtaining and managing certificates from Let's Encrypt can be found in the analysis document and in this blog post.