Prioritize https refreshes on TAL URLs

Prioritize https refreshes on TAL URLs

Few reasons:

1. rsync is a bit of a pain as a retrieval tool for RPKI,
   and I'd like to avoid it when I can get away with it.
2. Refresh by SIA was already prioritizing RRDP over rsync,
   so this makes the overall behavior more consistent.
3. Always preferring one protocol over the other tends to
   reduce bandwidth & cache usage.

So, mirror the SIA refresh order for TAs. From highest to lowest
priority:

1. Online HTTPS (including RRDP)
2. Online rsync
3. Fallback HTTPS (including RRDP)
4. Fallback rsync