Implement E2E testing in GitHub Actions

[dereknola]

Is your feature request related to a problem? Please describe.
We currently don't run all the E2E tests in Drone, due to a need to run tests sequentially (limitations around libvirt naming space).

Describe the solution you'd like
Run more of the E2E tests that only require a few nodes (1 server, 1 agent typically) in GitHub Actions. Utilize a matrix setup to parallelize testing.

Additional context

With the enablement of nested virtualization in GitHub Actions, it is finally possible to run a subset of the E2E tests there.