[feature request] Skip updating column descriptions

[brandonpeebles]

Feature:

Ability to skip updating column descriptions or the ability to specify what keys from the YAML you want to force inheritance for (e.g. progenitor, description, tags, etc.).

Use case:

Currently if I want to update certain column info like progenitor, I have to use --force-inheritance. This is normally fine, but sometimes there are cases where we add extra detail to a description in one model that isn't needed for that same column upstream.

The issue arises when we might change the source of one model perhaps for a cutover (e.g. ref('my_model') → ref('my_model_v2') and then I want to update the osmosis_progenitor metadata. If I run dbt-osmosis refactor it won't update the value since there's already something there. But if I force inheritance, I'll also overwrite any custom descriptions I might've added.

[z3z1ma]

This will now be the default behavior. Not overriding if a description exists. It was the original intention really.
Once #189 is merged. We might tag a 1.0.0 release with it.