Add ‘recipe system’ and ‘default content system’ subsystems and update Maintainers.txt

Problem/Motivation

In #3439923: Add recipes api as experimental API to core we added 4 recipes APIs to core. As a follow up, we need to identify and add subsystems on Drupal.org and subsystem maintainers in MAINTAINERS.txt. These maintainers have special roles in the governance structure and additional permissions, like the ability to adjust the Assigned field on behalf of others, assign issue credits in core, etc. See https://www.drupal.org/contribute/core/maintainers#subsystem for what this means.

The new APIs added were:

• Drupal\Core\Config\Action
• Drupal\Core\Config\Checkpoint
• Drupal\Core\Recipe
• Drupal\Core\DefaultContent

In this conversation in the Recipes channel of Drupal Slack, @alexpott determined that we need two subsystems, ‘recipe system’ and ‘default content system’. The Config Actions and Config Checkpoint issues can live in existing systems.

I think config actions can stay in config or config entity system… but I think we need ‘recipe system’ and ‘default content system’

Proposed resolution

• Add ‘recipe system’ and ‘default content system’ subsystems to Drupal.org.
• Identify the subsystem maintainers.
• Provide a patch to MAINTAINERS.txt (committers will do the followup tasks of assigning maintainer permissions, etc).

Remaining tasks

Do it.

User interface changes

API changes

Data model changes

Release notes snippet