Add `aws-cli` to our tools image build to be pulled in to agent images

The AWS CLI is used in the sonobuoy agent and will soon be used in the workload test agent. The source code for the AWS CLI is open source, located here:

https://github.com/aws/aws-cli

We should add this to the set of tools that are built in `tools/Dockerfile` so any agents that need this CLI can just copy it over. This also makes sure we are building from source rather than pulling down a binary directly.

Start with tools/Dockerfile and review how existing tools are built from source. Use the AWS CLI source repository linked in the issue as the upstream reference. Done means the tools image builds the AWS CLI from source and makes it available for agent images to copy.

Written by the indexing model from the issue text.