enables admin_role module

[markconroy]

Closes #748

What does this change?

Enables the new localgov_admin_role module, so we have a consistent way of working with an admin role.

How to test

Install the distro, check that there is now an 'Admin' role and that is set to be the role used for the administrator role.

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

[andybroomfield]

I'm getting the following error about missing the localgov_admin_role module, which is becuase I have a different branch of localgov_core checked out, but this reminds us that we should now bump up the minimum version of localgov_core in the profile to make sure the sub module it there.

Required modules:Required modules not found.<br /><br />The following modules are required but were not found. Move them into the appropriate modules subdirectory, such as <em>/modules</em>. Missing modules:   
                                                                                                                                                                                                                    
  <!-- THEME DEBUG -->                                                                                                                                                                                              
  <!-- THEME HOOK: 'item_list' -->                                                                                                                                                                                  
  <!-- 💡 BEGIN CUSTOM TEMPLATE OUTPUT from 'core/themes/claro/templates/classy/dataset/item-list.html.twig' -->                                                                                                    
  <div class="item-list--comma-list item-list"><ul class="item-list__comma-list"><li><span class="admin-missing">Localgov_admin_role</span></li></ul></div>                                                         
  <!-- END CUSTOM TEMPLATE OUTPUT from 'core/themes/claro/templates/classy/dataset/item-list.html.twig' -->         

[markconroy]

@ekes you requested changes in this. Is it okay for you now? Or is there more to do?