Move default search index and view into a "defaults" submodule

Problem/Motivation

This module provides a default search index and view to provide a default search experience for content. This assumes content types have a body field and caused #3218089: Could not retrieve data definition for field. The view also creates a main menu item and may not be desired #3207726: Disable Acquia Search view on install.

Proposed resolution

Move the configuration items in config/optional to a submodule. Search API does this with search_api_db_defaults

Remaining tasks

Move the config out of config/optional and make a new submodule.