MINOR: acme: extend resolver-based DNS pre-check to dns-persist-01

MINOR: acme: extend resolver-based DNS pre-check to dns-persist-01

Add challenge_type parameter to acme_rslv_start() to select the correct
DNS lookup prefix: _validation-persist.<domain> for dns-persist-01 and
_acme-challenge.<domain> for dns-01.

Default cond_ready to ACME_RDY_DNS|ACME_RDY_DELAY for dns-persist-01.
Extend ACME_CLI_WAIT to cover dns-persist-01 alongside dns-01.

In ACME_RSLV_READY, check only TXT record existence for dns-persist-01
since the resolver cannot parse multiple strings within a single TXT entry.