docs: Rename 'mail_alias' to 'mail-alias' in example config (#1346)

The example included an invalid character `_` for the attribute `name`

This resulted in:

```
Cannot create attribute with invalid name. Valid characters: a-z, A-Z, 0-9, and dash (-). Invalid chars found: _
```

This fixes the example by using a `-`.

example_configs/bootstrap/bootstrap.md

@@ -130,7 +130,7 @@ Fields description:
     "isVisible": true
   },
   {
-    "name": "mail_alias",
+    "name": "mail-alias",
     "attributeType": "STRING",
     "isEditable": false,
     "isList": true,
@@ -291,4 +291,4 @@ spec:
                   items:
                     - key: group-configs.json
                       path: group-configs.json
-```
+```