Asg capacity rebalancing & EMR updates

[ivallhon]

Description of changes: This PR updates the EC2 Auto Scaling with multiple Instance types and purchase options workshop:

• Update the Spot resilience page to include Capacity Rebalancing best practices, leaving custom interruption handler as an optional exercise to suit other use cases where Capacity Rebalancing may not be the best fit (e.g. queue workers) - Update Auto Scaling workshops to use Capacity Rebalancing #134
• Update workshop weights to position the short version first and Running EC2 Workloads at scale at the bottom, as this is a shorter version that's preferable for Spot-only (and remote) events.
• Update to AWS CLI 2.x

EMR Workshop updates:

• Modify screenshot for Instance fleets to include the allocation strategy
• Add a step to remove AWS CLI 1.x before installing AWS CLI 2.x
• Add instructions for SSH tunneling via Cloud9

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