Pass extra argument during docker build for `pongo build`

[DingGGu]

Support pass extra argument to pongo build will helpful other integration. https://github.com/Kong/kong-pongo-action/issues/3

[Tieske]

should the user specify options to pass-through to docker, or should we create a Pongo option to hold the cache location (which wraps the docker internals then).

wdyt?

[DingGGu]

In my opinion, kong-pongo makes it possible to pass arguments, and kong-pong-action supports the cache option for easy setup.