Add MVP of automated performance tests (#3953)

## Motivation and Context
<!--- Why is this change required? What problem does it solve? -->
<!--- If it fixes an open issue, please link to the issue here -->
We have an EOY goal to to integrate with our internal automated
performance monitoring solution.

## Description
<!--- Describe your changes in detail -->
Add a new crate at `aws/sdk/benchmarks/sdk-perf/` that runs some very
basic performance tests (currently just serializing and deserializing
DDB request/responses). Also add a new ci-script that generates the
correct SDK crates, compiles the `sdk-perf` crate, and creates a shell
script that the automated performance tests invoke to kick off our
tests.

## Testing
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to -->
<!--- see how your change affects other areas of the code, etc. -->
I deployed this code to my personal Catapult instance (along with the
changes to our internal CDK that will be CRed separately) and
successfully ran an `e2e-test`.

## Checklist
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rather than leaving it unchecked -->
No customer visible changes, this is strictly for our CI.

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Author: landonxjames