executor: Make fake task for better observability

Created by: efritz

There's a portion of code that has no UI-visible step. We should make a fake step and report it as if it's running a command, although it might be doing some Go/syscall-driven file movement to prep for firecracker execution.

Having this will help us figure out how to reduce latency for tasks.

Relevant places to measure:

• Copy the file contents from the job record into the working directory
• Same with scripts
• run lock may be something we're waiting on? Maybe should expose this as a run log as well