Rather than adding intermediates in the certificate bundle we now
validate the leaf certificate with intermediates as untrusted (used for
chain building only).  Only the root certificates are used as trust
anchor.

Not pining intermediate certificates anymore is in line with Let's
Encrypt's latest recommendations:

    Rotating the set of intermediates we issue from helps keep the
    Internet agile and more secure.  It encourages automation and
    efficiency, and discourages outdated practices like key pinning.
    “Key Pinning” is a practice in which clients — either ACME clients
    getting certificates for their site, or apps connecting to their own
    backend servers — decide to trust only a single issuing intermediate
    certificate rather than delegating trust to the system trust store.
    Updating pinned keys is a manual process, which leads to an
    increased risk of errors and potential business continuity failures.
    — https://letsencrypt.org/2024/03/19/new-intermediate-certificates:

lacme(8): for --config=, --socket=, --config-certs= (and ‘socket’/
‘config-certs’/‘challenge-directory’ configuration options *before*
privilege drop; and for the [accountd] section ‘command’/‘config’
configuration options *after* privilege drop).

lacme-accountd(1): for --config=, --socket= and --privkey= (and
‘socket’/‘privkey’ configuration options).

This also changes the default configuration file location.  lacme(8) and
lacme-accountd(1) now respectively use /etc/lacme/lacme.conf resp.
/etc/lacme/lacme-accountd.conf when running as root, and
$XDG_CONFIG_HOME/lacme/lacme.conf resp. $XDG_CONFIG_HOME/lacme/lacme-accountd.conf
when running as a normal user.  There is no fallback to /etc anymore.

This is useful for enabling the snippet with `a2enconf lacme`, cf.
https://bugs.debian.org/955859 .

Cf. https://community.letsencrypt.org/t/staging-hierarchy-new-root-cert/145677 .