run full l4v on AWS

[lsf37]

trigger a full l4v regression test build for a matrix of architecture on AWS, report results through GitHub status.

Since this costs money, it'll need some access control, either org members only for PR, or triggered by label.

[lsf37]

There are a bunch of options for how to trigger an AWS run. Some requirements:

• needs access control, i.e. manual/restricted trigger shouldn't be circumventable by adding/changing code in the repo. Could be via secrets or different ways of invoking the action, or by using a webhook and doing the entire rest on AWS

• needs ability to spin up and shut down test runners on demand

• should have a global max number of runners to limit cost rate

• needs a hard timeout

• would be nice to treat separate architectures as completely separate runs for reporting (not like Bamboo currently)

• would be nice to see intermediate log output