Authorities (e.g. Let's Encrypt) usually have Terms of Serivce (ToS)
that have to be agreed to. Up until this point we automatically
indicated agreement to those ToS and sent the necessary value.
This commit changes the behaviour to be in line with recommendations
from Let's Encrypt that the user themselves have to indicate their
agreement by no longer automatically doing so (except for cases of
legacy configuration files to provide compatibility).
The user can now indicate ToS agreement by either setting the associated
configuration variable (authority_tos_agreement) to the required value
and/or providing the required value via a command-line parameter
(--authority-tos-agreement=<value>/--tos-agreement=<value>/--tos=<value>)
