Add support for minvcpu and desiredvCpus to context

[KevinSayers]

Description

Currently the context supports specifying the maxVCpus, further support for minVCpus and desiredVCpus would enable greater control over the compute environment.

This could be modified in the Console, but it feels disjointed.

Use Case

Deploy a context so that the Batch compute env has a minimum number of vcpus available. In particular this would be beneficial for iterative test runs.

Proposed Solution

Add the minVCpus and desiredVCpus fields to the context.

Other information