Add warning to ref guide that using "properties.name" is an expert option

This came to light when I was looking at two user-list questions where people try to manually define core.properties to define replicas in SolrCloud. There are two related issues:

1> You can do things like "action=CREATE&name=eoe&property.collection=blivet" which results in an opaque error about "could not create replica....." I propose we return a better error here like "property.collection should not be specified when creating a collection". What do people think about the rest of the auto-created properties on collection creation?

coreNodeName
collection.configName
name
numShards
shard
collection
replicaType

"name" seems to be OK to change, although i don't see anyplace anyone can actually see it afterwards....

2> Change the ref guide to steer people away from attempting to manually create a core.properties file to define cores/replicas in SolrCloud. There's no warning on the "defining-core-properties.adoc" for instance. Additionally there should be some kind of message on the collections API documentation about not trying to set the properties in <1> on the CREATE command.

<2> used to actually work (apparently) with legacyCloud...