Allow conditional control over lazy-loading database notifications

[jackwh]

Description

Something of a followup to #13321 , this backwards-compatible PR simply adds a new option to control whether database notifications are lazy-loaded when enabled.

The rationale behind this is simply that it forces an extra server roundtrip on every page load, and for many apps, that's just unnecessary overhead.

Visual changes

N/A

Functional changes

• Code style has been fixed by running the composer cs command.
• Changes have been tested to not break existing functionality.
• Documentation is up-to-date.

[danharrin]

Thanks