[Operator] Dataplane spec is mandating to have allocationStrategy in the spec

[hakuna-matatah]

• Dataplane spec is mandating to have allocationStrategy in the spec. If not provided it will run into the following issue:

message: "creating auto scaling group for s-9a7d13d2-e635-4418-8852-7d528e66fa69,
     ValidationError: 1 validation error detected: Value '' at 'mixedInstancesPolicy.launchStrategy.onDemandAllocationStrategy'
     failed to satisfy constraint: Member must have length greater than or equal
     to 1\n\tstatus code: 400, request id: 270dd3de-8aa9-4ff2-baeb-81ac9cfd1fd0"
   status: "False"
   type: Active

We need to look into why defaulting doesn't work. If we plan to remove defaulting, we need to update the example spec here] with allocation strategy

[prateekgogia]

Fixed in #75