handles: consider clarifying that TXT data could be comma-separated

[bnewbold]

The value (data) of a handle resolution DNS TXT record is currently did= followed by the DID itself, eg did=did:plc:abc123.

This follows a somewhat-common syntax for DNS data which can be a list of key/value pairs separated by comma (no whitespace). If we want that syntax for handle resolution, we should clarify it in the specs. Specifically that there might be multiple values, and that the DID might not be the first value.

Relatedly, we might want to make the did= be optional if there is only a single value.

Had these thoughts while reading through: https://datatracker.ietf.org/doc/draft-ietf-dnsop-domain-verification-techniques/

[bnewbold]

thought this through at some point, and think these changes would be bad/non-sensical. closing.