Optionally add curated list of configuration to install profile

Problem/Motivation

Currently we're adding settings from the default and admin themes to the install profile, #2600566: Optionally add settings for default and admin theme to profile.

There are several other configuration items that would be candidates for adding. Previously doing so was blocked by #2443589: Offer ability to add configuration overrides to install profile, but the initial commit in that issue has enabled adding extension-provided configuration to the install profile.

Proposed resolution

Convert the existing 'theme' setting into 'curated' (parallelling the 'curated' setting in the 'exclude' assignment plugin). Following core's Standard install profile, which also adds these, add the following items:

automated_cron.settings
system.cron
system.theme

Remaining tasks

User interface changes

API changes

Data model changes