[META] Document core config actions with examples in phpdocs

Problem/Motivation

Most core config actions lack documentation. E.g. see namespace namespace Drupal\Core\Config\Action\Plugin\ConfigAction.

I assume we have change records for most of them, but would be useful having phpdocs with recipe usage examples.

A good documented one as a reference is CreateForEachBundle.

Proposed resolution

Fix phpdocs for config actions, using CreateForEachBundle as a reference.

Remaining tasks

Create child issues, as we might want the different subsystem maintainers to review/approve.

User interface changes

None.

Introduced terminology

None.

API changes

None.

Data model changes

None.

Release notes snippet

None.