Support for building Windows AMIs

[jschwartzentruber]

For some projects, we will need to maintain Windows AMIs in the same way as we maintain Docker images.

community-tc-config already has support for applying a bootstrap script to an existing AMI and taking a snapshot. We could implement this in orion instead as another service type.

This is different from existing services:

• artifacts live in EC2, not TC.
• "build" tasks would work with an external EC2 instance.

The following needs to be implemented:

• Create an EC2 instance, apply a bootstrap script, and take a snapshot. The resulting AMI id(s) should be in an artifact of the task. It may be possible to reuse laniakea for this.
• Copy the resulting instance to other regions.
• Share the instance(s) with another AWS account. (eg. community-tc)
• Update TC pools that use the AMI to use the new one. (trigger fuzzing-tc-config)
• Delete old AMIs.

The external EC2 instance could be lost if task exception or failure occurs, so we would need a periodic hook to check for and remove orphans.

In the future this may need to support GCE or Azure VMs, but for now we only run Windows instances in EC2.