CLI plugin sample

[mattmoor]

We discussed this in the TOC review last week, but the idea was that we should include the skeleton of a CLI plugin for a source alongside the source, and that to make this template comprehensive that we should have a sample source plugin here for that.

cc @rhuss

[rhuss]

We already have a skeleton for a generic plugin at https://github.com/knative/client-contrib/tree/master/plugins/hello but I think it would make a lot of sense to add one specific for source, including the CLI conventions which also apply to source plugins.

[rhuss]

/assign

[github-actions]

This issue is stale because it has been open for 90 days with no
activity. It will automatically close after 30 more days of
inactivity. Reopen the issue with /reopen. Mark the issue as
fresh by adding the comment /remove-lifecycle stale.

[lberk]

/remove-lifecycle stale

[github-actions]

This issue is stale because it has been open for 90 days with no
activity. It will automatically close after 30 more days of
inactivity. Reopen the issue with /reopen. Mark the issue as
fresh by adding the comment /remove-lifecycle stale.

[rhuss]

/remove-lifecycle stale

[github-actions]

This issue is stale because it has been open for 90 days with no
activity. It will automatically close after 30 more days of
inactivity. Reopen the issue with /reopen. Mark the issue as
fresh by adding the comment /remove-lifecycle stale.

[rhuss]

/remove-lifecycle stale