Turn epic table of `imagePullPolicy` overrides into real docs

Currently the epic description contains a table with packages, default image pull policies, and available overrides.

We should turn this into a doc in our BB repo under https://repo1.dso.mil/platform-one/big-bang/bigbang/-/tree/master/docs/guides/using_bigbang (i.e. image_pull_policy.md). This will provide us with a good reference for customers to be able to handle these overrides - as well as help us in future issues for the epic.

AC:

• Table from the epic modified/added to BB docs