20200918FG: tune Makefile, make it generic and functional from top level

OK, now we have a leaner Makefile and even a nice generalisation of it, so that it's easy to tune parameters, f.i.:

• time make KOMPOSE=kompose deploy ## i.e. it now allows to override kompose name, version, namespace...

caveat # 1: there is still an issue with ports over k8s, I'll treat that separately

caveat # 2: I had to make Makefiles hardlinked instead of symlinked to get to play with kompose/1.21 (THAT was triggering the previous errors!), hoping it would finally work and overcome the above bug; it hasn't yet, but I will come back to it.

@martinfontanet : review on your end & merge on your !10 (merged), asap please?