source apiserver update --resource should follow the common update semantics for list like structures

[rhuss]

I.e. the same as for kn service update --env or kn trigger update --filter. I.e. add new resources, overwrite existing, and remove when suffixed with -.

[rhuss]

While fixing this, this handling should be put into a shared method so to guarantee the list-like options are handled the same.

[daisy-ycguo]

/assign daisy-ycguo
I would like to take this issue.