Create a common snippet for breaking changes for model contracts

[dbeatty10]

Contributions

• I have read the contribution docs, and understand what's expected of me.

Link to the page on docs.getdbt.com requiring updates

There are two pages with common language that has slightly diverged (search for "Removing an existing column"):

1. website/docs/docs/collaborate/govern/model-contracts.md
2. website/docs/reference/resource-properties/versions.md

Some of the behavior has changed across versions (e.g. v1.6 and 1.9), so that makes it a little tricky to figure out how best to write this, especially since <Version> blocks have an awkward extra newline when they are with a list of bullet points.

What part(s) of the page would you like to see updated?

It looks like we can combine these two to share the same snippet:

https://docs.getdbt.com/reference/resource-properties/versions#detecting-breaking-changes

https://docs.getdbt.com/docs/collaborate/govern/model-contracts#how-are-breaking-changes-handled

Additional information

See #6119 (review)