better support for jx help

[jstrachan]

right now jx help doesn't work great with plugins. e.g. this doesn't work:

jx help pipeline start

however this does

jx pipeline start --help

which basically runs jx-pipeline start --help directly on the jx-pipeline plugin

it would be great to implement jx help foo bar as an alias for jx foo bar --help

[jenkins-x-bot]

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/lifecycle stale

[jenkins-x-bot]

Stale issues rot after 30d of inactivity.
Mark the issue as fresh with /remove-lifecycle rotten.
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/lifecycle rotten