[Proposal]Support for Multiple Node Pools

[samcgardner]

Hi,

We use GKE and are interested in deploying node pool shifter, but are being stymied by the fact it can only shift to/from a single node pool pair at a time. Obviously we could deploy it twice, but it seems to make more sense to allow an arbitrary list of pairs of node pools to shift between. I'm happy to PR such a change, would you be willing to accept it?

Thanks for all the great work the estafette project does :)

[sangamgo]

@samcgardner we are also actually in the same situation as yours, is this done on your end, if yes, could you please suggest us what you did?