Move some channel properties to channel parameters

Sergey and I discussed it already via zoom but we figured out that:

hst:linkurlprefix (string)
hst:cdnhost (string)

are in the same boat as the 'spaUrl' : The spaUrl was decided to have to be manageable via parameter info properties / settings (if possible a system parameter which cannot be removed). But having the spaUrl as parameter and having hst:linkurlprefix and hst:cdnhost as channel property (only modifiable via REST API) doesn't make sense: the 'linkurlprefix' get prefixed to every SPA link, so if that is still, say, spa.bloomreach.com, then if you set spaUrl to localhost:3000, the spa will not run nicely locally since the linkurlprefix still is spa.bloomreach.com, and same goes for cdnhost.

Therefore, I recommend that

hst:linkurlprefix (string)
hst:cdnhost (string)

get removed from the hst-types.cnd from [hst:channel] node but get supported as system (default available) channel parameter. Since this is a separate task from this issue, I'll create a new issue for this

Note that although linkurlprefix and cdnhost will be managed as parameter info properties, the Channel object still can (should) just have the methods

#getLinkUrlPrefix()
# getCdnHost()

so I think we should keep those getters as-if the properties are still first class citizen props of the channel object, just like spaUrl will be