change HAIP to mandate DCQL

[Sakurann]

looks like rough consensus in the WG is to encourage implementers to use DCQL, so probably makes sense to change HAIP to mandate DCQL (currently PE)

this would also address #27 I think

[c2bo]

Should be mandatory imho for both:

• DC API
• "normal" https flow

[tlodderstedt]

WG call 07.1.2025: making DCQL MTI makes sense. @c2bo does the PR.