Snapshot configuration as installed and updated from recipes and extensions

Problem/Motivation

Determining what configuration updates are available from installed extensions requires a baseline to compare against and to use for 3-way merges (see #2960874: Support 3-way configuration merging → ).

The Configuration Synchronizer contrib module provides a relevant approach via the Configuration Snapshotter module.

Proposed resolution

Adapt from Configuration Synchronizer:

• Storage service
• Snapshotter interface and service
• Lister service
• Snapshotter event subscriber
• Implementation of hook_modules_installed() and hook_themes_installed()

Apply all config actions to the snapshot storage as well as to the active config storage.

Remaining tasks

User interface changes

API changes

Data model changes