Enable no conflict installation mode

Problem/Motivation

Core's configuration install API prevents enabling an extension that provides any configuration item that already exists on the site.

This behaviour is a sensible default, but there are certain use cases it interferes with, including:

• Install a new module providing configuration on the originating site.
• Install a module providing configuration on a site installed with an install profile that already provided configuration in the module.

Proposed resolution

Introduce a configurable option to allow reprovision of configuration.

TBD: in the case that configuration is reprovided, what of the following is the expected default?

• The existing configuration in the active storage is retained unaltered.
• The reprovided configuration overwrites what's in the active storage.
• The reprovided configuration is merged into the active storage in such a way as to respect customizations.

Remaining tasks

User interface changes

API changes

Data model changes