Add an intermediate command between pc init and pc run to buid app

[evandeng2009]

Describe the bug pc run takes too much time before fully start the app for the 1st time, especially for the dokcer. I'd like to add an intermediate command, like pc buid which will be exectute in Dockerfile before pc run, to make the app really ready in advance, as for the 2nd start, it's pretty quick.

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