Add dedicated permission for administering module settings

Problem/Motivation

At the moment the module uses the generic access administration pages permission from Drupal core to restrict access to /admin/config/content/elb. In some site implementations it is desirable to have a distinct permission to limit access to the ELB settings.

Steps to reproduce

Add the permission access administration pages to a user that has no access to other pages that touch Drupal configuration, for example. Witness the menu item appear for users in that role.

Proposed resolution

Add a distinct permission dedicated for administering the settings of this module only.

Remaining tasks

• Add the elb.permissions.yml file with the correct permission
• Switch the permission used in elb.routing.yml for route elb.ext_link_blocklist_settings_form
• (optional) write an update hook implementation in elb.install that adds the new permission to all roles that have the previous permission

User interface changes

None

API changes

None

Data model changes

None