Add API call for frontend to fetch list of valid roles from backend

- only relevant for admin config (addUser, editRole)
- admin only (double-checked)

web/frontend/src/config/AdminSettings.svelte

@@ -8,6 +8,7 @@
     import Options from './admin/Options.svelte'
 
     let users = []
+    let roles = []
 
     function getUserList() {
         fetch('/api/users/?via-ldap=false&not-just-user=true')
@@ -17,19 +18,32 @@
         })
     }
 
-    onMount(() => getUserList())
+    function getValidRoles() {
+        fetch('/api/roles/')
+            .then(res => res.json())
+            .then(rolesRaw => {
+                roles = rolesRaw
+        })
+    }
+
+    function initAdmin() {
+      getUserList()
+      getValidRoles()
+    }
+
+    onMount(() => initAdmin())
 
 </script>
 
 <Row cols={2} class="p-2 g-2" >
     <Col class="mb-1">
-        <AddUser on:reload={getUserList}/>
+        <AddUser roles={roles} on:reload={getUserList}/>
     </Col>
     <Col class="mb-1">
         <ShowUsers on:reload={getUserList} bind:users={users}/>
     </Col>
     <Col>
-        <EditRole on:reload={getUserList}/>
+        <EditRole roles={roles} on:reload={getUserList}/>
     </Col>
     <Col>
         <EditProject on:reload={getUserList}/>