In Access settings tab let users choose to make their data public

Nobody has claimed this yet.

Haven't added it yet as it's rarely needed.

* Add a new global setting "allow_anonymous_access"
* In Access Settings template show form (see below) to enable this feature => after successful change of setting value we should trigger a user re-sync
* In AccessSettings class process that form post and configure the above global setting accordingly
* Capabilitiy class needs to add the `MATOMO_VIEW` capability to all users when feature is enabled
* User Sync needs to make sure to enable/disable anonymous access in Matomo by giving the anonymous user view access

Tests for all of this...

The form could look like this

```html

Public access: Give everyone view access to your reporting data - including not logged in users

Enabling this feature makes your reports available to everyone. Anyone will be able to view how many visitors you had, what pages have been viewed on your website how often, and more.
Learn more about making your report data public and viewable by anyone

Are you sure you want to change anonymous's role to View for your reports?
Giving the anonymous user the View role will make this website's data public and available to everyone, even if they do not have a Matomo login. Please type OK to confirm this change

```

Locate the Access Settings template, AccessSettings, Capability, and User Sync implementations, then trace how global settings and user roles are currently handled. Add the anonymous-access setting and confirmation form, update capabilities and synchronization when it changes, and add tests covering the setting, form handling, capabilities, and anonymous user's view access.

Written by the indexing model from the issue text.