docs(resource/role_mapping): indent sub-elements of role_assignments (#918)

In the context of the `federated_settings_org_role_mapping`, `group_id`
and `roles` are only meaningful as sub-elements of the
`role_assignments` field. This simply indents them accordingly.

Co-authored-by: Zuhair Ahmed <[email protected]>

Author: Horgix

website/docs/r/federated_settings_org_role_mapping.html.markdown

@@ -41,11 +41,11 @@ resource "mongodbatlas_federated_settings_org_role_mapping" "org_group_role_mapp
 * `org_id` - Unique 24-hexadecimal digit string that identifies the organization that contains your projects.
 * `external_group_name` - Unique human-readable label that identifies the identity provider group to which this role mapping applies.
 * `role_assignments` - Atlas roles and the unique identifiers of the groups and organizations associated with each role.
-* `group_id` - Unique identifier of the project to which you want the role mapping to apply.
-* `roles` - Specifies the Roles that are attached to the Role Mapping.
-  Available role IDs can be found on [the User Roles
+    * `group_id` - Unique identifier of the project to which you want the role mapping to apply.
+    * `roles` - Specifies the Roles that are attached to the Role Mapping. Available role IDs can be found on [the User Roles
   Reference](https://www.mongodb.com/docs/atlas/reference/user-roles/).
 
+
 ## Attributes Reference
 
 In addition to all arguments above, the following attributes are exported: