Allow users to specify number of replicas of a given node type

[anishasthana]

Existing format: orderedinstance: m5.4xlarge_g4dn.xlarge
Proposed format: orderedinstance: m5.4xlarge_g4dn.xlarge:255

We currently use _ to separate instance types. Our proposal is to add :<int> as a valid portion of the string to allow users to easily specify the number of nodes they require of a given type.

[asm582]

Thanks for creating the issue, We also need to make sure that we check quota limits before we scale-up with the new scheme.

@MichaelClifford @Maxusmusti some new changes on the SDK side that we see coming soon