Support Channel CRUD operations

[rhuss]

Feature request

Knative eventing channel should be able to be managed with a kn channel family of command.
They should implemented similar to the management of triggers or brokers.

Use case

Manage Channels for creating a Knative Eventing topology

UI Example

# Create a channel
kn channel create mychannel --type kafka

# Update a channel
kn channel update mychannel ...

# Delete a channel
kn channel delete mychannel

# List all channels
kn channel list mychannel

# Show details of a channel
kn channel describe mychannel

[navidshaikh]

/assign