Support collectors on a `command` in a `TestSuite`

[porridge]

Not sure if I got this right (the docs seem to be a little stale), but it sounds to me like collectors can currently only be specified on a TestAssert which in turn can only be specified on the NN-assert.yaml level.

It would be great if they could also be specified on a command specified in a kuttl-test.yaml.

Otherwise one needs to do ugly things like:

• wrap a command in an extra shell script which does if ! main-command; then dump some debug info;fi, or
• artificially set ignoreFailure: true on the command and then add another subsequent command which checks state and dumps debug info before failing.

Originally posted by @porridge in https://github.com/kudobuilder/kuttl/issues/174#issuecomment-660968971

[kensipe]

yeah... I meant to re-open the original post after the updated collectors landed... in order to capture this... but capturing the addition details here seems better! thanks for following it up!