Allow set_service to add or override files

[jshufro]

Background & motivation

After importing a plugin and applying it to the plan, it would be useful if I could call set_service to replace or add file artifacts to the services in the plan.

As an example, ethereum-package creates a grafana service, but doesn't expose any way to update grafana.ini.

Desired behaviour

set_service should allow file artifact modification

How important is this to you?

Painful; the lack of this feature makes using Kurtosis frictionful.

What area of the product does this pertain to?

Other: anything not covered by the above