riff function create should optionally wait until the service reaches a success or error state

[glyn]

By default, riff function create logs success after creating the ksvc:

$ riff function create ...
...
riff function create completed successfully

Subsequently, problems may occur and the ksvc may never reach a good state. The status may be checked using riff service status.

So that the user does not need to check the service status manually, a --wait switch is introduced which causes the command to block until the service reaches either a successful or an error state.

An example of success:

$ riff function create node square ... --wait
...
riff function create completed successfully

An example of an error:

$ riff function create node square ... --namespace badnamespace --wait
...
Error: function create failed: RevisionMissing: Configuration "square" does not have any ready Revision.; Revision "square-00001" failed with message: "build step \"build-step-build-and-push\" exited with code 1 (image: \"docker-pullable://gcr.io/kaniko-project/executor@sha256:4ba457d5c73a085358d2062152dc739ff2e96f4290412136a1efae8dca1a7501\"); for logs run: kubectl -n default logs square-00001-d2vxs -c build-step-build-and-push".

The wording of the completion message when --wait and --verbose are not specified, should also be adjusted, e.g.:

$ riff function create node square ...
...
riff function create completed successfully
Issue `riff service status square` to see the status of the function