feat: add skipping pulls by default if present, add --force flag and return on pull error

[tylerslaton]

Doing three things:

1. Returning errors from the pull so the program closes out when reaching an error there
2. Adding logic to skip pulling if the image is already present locally
3. Adding a new --force flag that forces a pull to occur even if the image is present locally

Note: I started to implement a test for this but was hitting some unexpected complexity when attempting to pull an image within a test. I'll have a follow-up that introduces some refactors to make that form of testing easier.

Closes #43

[exdx]

Closes #43

[exdx]

This is good, a lot closer to what I had in mind originally. A few nits but I think this is largely good to go.