Provide configuration to define when config changes are pushed to servers in a domain

An EAP customer request:

Right now, any changes done via the CLI to an active profile are pushed to all instances immediately. Some go life, some at reload only
While batch mode can be used to bundle a number of changes in one go, there is currently no way to tell individual servers or server-groups when to accept updates or not.
This proposal is to allow a config switch on servergroup level and on individual server level to accept a configuration change selectively:
1. immediate, the current situation, being the default
2. at restart only
3. at explicit being told so, e.g. when a "reload" is ordered
Example:
<server name="server-three" group="other-server-group" updates="immediate">
the default when the attribute is absent
<server name="server-three" group="other-server-group" updates="start">
<server name="server-three" group="other-server-group" updates="explicit">
The latter could then be triggered with:
/host=master/server-config=server1:reload
Similar option could be set on servergroup level, with a similar reload command on that level