MINOR: ssl/crtlist: split the ckch_conf loading from the crtlist line parsing

MINOR: ssl/crtlist: split the ckch_conf loading from the crtlist line parsing

ckch_conf loading is not that simple as it requires to check
- if the cert already exists in the ckchs_tree
- if the ckch_conf is compatible with an existing cert in ckchs_tree
- if the cert is a bundle which need to load multiple ckch_store

This logic could be reuse elsewhere, so this commit introduce the new
crtlist_load_crt() function which does that.