CLI: add support for experimental new filters API in trigger

[Cali0707]

Feature request

As part of preparing the experimental new filters API to Beta (tracked here: knative/eventing#5204), we should add support to kn to create these filters when creating a trigger.

Use case

With the new filters API entering Beta, more users will want to try it out. It would be convenient for them if they can use kn to create them, instead of being required to use yaml files to try out the new filters.

UI Example

kn trigger create mytrigger --new-filter filtertype=filtervalue

[Cali0707]

@pierDipi @dsimansk @rhuss any thoughts on this?

[dsimansk]

@Cali0707 +1.

There's only support to display new filters, but not build/define. #1794

Of course the tricky part is designing smooth UI elements for so many combinations possible.

[pierDipi]

@Cali0707 +1.

There's only support to display new filters, but not build/define. #1794

Of course the tricky part is designing smooth UI elements for so many combinations possible.

+1, we can also consider not supporting everything in the CLI as a starting point and reconsider later

[rhuss]

Could be a good candidate for the 48h Knative hackathon.

[JuneOh710]

/assign