[Tagging] Adding values to usage=* key for power transmission

[Rainer Fügenstein]

hi,

FL> I knew usage=* and it can be the ideal key to indicate usage=transmission,
FL> usage=distribution,... on power lines or power cables.

If I'm not mistaken, this key is intended to serve  the same purpose
as the network=* key is in the pipeline proposal:
https://wiki.openstreetmap.org/wiki/Proposed_features/PipelineExtension#Pipelines

FL> But it is currently and exclusively used for railway tagging.
FL> https://wiki.openstreetmap.org/wiki/Key:usage

concerns against using the network=* key have been raised. it would
make sense to join forces here and use a common key, be it usage=* or
something else.

cu