introduce fixed ChannelIDs to send data and make the channelnames updateable

[mhengl]

Is your feature request related to a problem? Please describe.
using channelIDs instead of Channelnames to adress the target channels one can utilize the payload path to update channelnames and synchronize values more easily.

Describe the solution you'd like
add ChannelID's to the PRTG-Channel-Definitions and allow them to be send to compatible PTRG instances, configurable with a config property

Describe alternatives you've considered
always send channelIDs but break with older PRTG Versions

Additional context
A Bug in PRTG has to be resolved first, not allowing channelIDs for dynamic channels over HTTP Push based Sensors