feat: add `labgrid_binary`

The labgrid_binary rule allows running an executable within the labgrid environment specified by the platform attribute:

labgrid_binary(
    name = "printenv",
    src = "@ape//ape:printenv",
    platform = "@rules_labgrid//labgrid/platform:localhost",
)

As it's an executable rule, you can use it with bazel run:

$ bazel run :printenv -- LG_STATE
shell

Closes #25 (closed).

Testing

I haven't been able to write end-to-end tests for this because of #31 (closed), but I've tested it manually.