allowing configuring how many top tasks per row

[markconroy]

Closes #897

What does this change?

Add a configuration option for how many top tasks we want to show per row for service landing pages, with the default being 4-in-a-row.

Currently we have 3, so will need to have a note on the release notes that to keep the same feature we currently have, you will need to go to your theme settings and set it to 3 then save the form and export the config.

How to test

• Go to theme settings page
• Scroll to bottom
• Set how many items per row for top tasks

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Thanks to Big Blue Door for sponsoring my time to work on this.

[willguv]

We need the new sites to have 4 top tasks per row, but we don't want the existing sites to change. They need to opt in to new stuff

@markconroy proposed a helper module a while back for LG Base to apply updates - I think we need to seriously consider this as there will be many more changes like this in the future eg when we follow GOV.UK or NHS design system changes

@tonypaulbarker seconds this approach

[markconroy]

PR to add updates module: #900

We'll also need to have the module enabled.

[markconroy]

https://www.drupal.org/project/localgov_base/issues/3563416