Allow adding to "General System Information" on "Status report"

Problem/Motivation

On the "Status report", the five boxes in the "General System Information" are hard-coded in status-report-general-info.html.twig. This means that if a developer wants to add a box, they need to override this template. There should be an easier way.

Example use case: We are making a custom web app for a client. We want the version and other information about the app prominently displayed on the status page. We currently use hook_requirements() to add this to the "Checked" section of "Status Details". We would like something more prominent.

Proposed resolution

Refactor status-report-general-info.html.twig so that it is looping through an array of items. Setup the items in a preprocess function. This allows developers to add to this section in their own preprocess function.

Remaining tasks

Agree on how it should work. Implement.

User interface changes

None.

API changes

None, except that sections can be added via preprocess.

Data model changes

None.

Release notes snippet