MINOR: ssl/cli: "acme ps" shows the acme tasks

MINOR: ssl/cli: "acme ps" shows the acme tasks

Implement a way to display the running acme tasks over the CLI.

It currently only displays a "Running" status with the certificate name
and the acme section from the configuration.

The displayed running tasks are limited to the size of a buffer for now,
it will require a backref list later to be called multiple times to
resume the list.