Add capacity recommendations to dynamodb-lens

[anorth848]

On-Demand capacity mode for DynamoDB allows unpredictable workloads to avoid throttling (ish), but this stability comes at a cost.
It is significantly more expensive than Provisioned in most cases.
There are many scenarios where On-Demand is unnecessary or a provisioned table will flat-out be cheaper.

We can present various configurations and the associated cost savings estimates and risk levels of switching to provisioned.

For example, switching to Provisioned Throughput mode with:
MIN/MAX Autoscaling WCU/RCU settings
P33 MIN/P100 MAX Autoscaling WCU/RCU settings
P50 MIN/P100 MAX Autoscaling WCU/RCU settings
P90 MIN/P100 MAX Autoscaling WCU/RCU settings
P100 static WCU/RCU settings
Also, each scenario above with 1 and 3-year reserved capacity