Add documentation for two new directives in the acme section:
- challenge-ready: configures the conditions that must be satisfied
before notifying the ACME server that a dns-01 challenge is ready.
Accepted values are cli, dns and none. cli waits for an operator
to signal readiness via the "acme challenge_ready" CLI command. dns
performs a DNS pre-check against the "default" resolvers section,
not the authoritative name servers. When both are combined, HAProxy
waits for the CLI confirmation before triggering the DNS check.
- dns-delay: configures the delay before the first DNS resolution
attempt and between retries when challenge-ready includes dns.
Default is 300 seconds.