Epic: Make contrib default

[Kircheneer]

Currently, the documentation is a mix of legacy and contrib approaches to building SSoT integrations. We need to unify this into a clear vision and also reflect this in the import paths. We need to provide enough features to handle most of the use cases and then clearly position the set of functionality as the default.

Related issues:

• Overhaul docs #468
  • revamps SSoT cookie for contrib pattern cookiecutter-nautobot-app#203
• Allow not controlling all objects in many-to-many relationship with contrib #592
• Update Contrib to use bulk CRUD operations for Django database models #482
• Document DataMapping and auto-populate it in nautobot_ssot.contrib.NautobotAdapter #235
• Document how to achieve things like the primary IP (with the challenge regarding order of operations)

An open question remains whether it should also be the default for syncs from Nautobot to a remote system. It provides less benefit there (only the load method for the source adapter).