Nested user attributes not exposed as valid LDAP attributes in LDAP Outpost

**Describe the bug**
When exposing custom attributes via the LDAP outpost, nested attributes are not returned as individual LDAP attributes. Instead, they appear in a serialized map format that does not seem to comply with LDAP.

**To Reproduce**
Steps to reproduce the behavior:

1. Configure a user in Authentik with a custom attribute containing nested values, e.g. settings.locale = en.
2. Query the user via the LDAP outpost using ldapsearch.
3. Inspect the LDAP response.

See that the attribute is returned as a serialized map string rather than as a proper multi-valued LDAP attribute.

**Expected behavior**
I would expect the LDAP outpost to flatten or map the nested attribute into standard LDAP attributes, for example:

```
settingsLocale: en
```

or

```
settings.locale: en
```

instead of:

```
settings: map[locale:en]
```

**Version and Deployment (please complete the following information):**

- authentik version: 2025.8.3
- Deployment: Docker

**Additional context**
Add any other context about the problem here.

Start by reproducing the LDAP outpost response with ldapsearch using a user custom attribute containing a nested value such as settings.locale. Inspect how the LDAP outpost represents that attribute, then verify that nested values are exposed as valid individual or multi-valued LDAP attributes rather than a serialized map string.

Written by the indexing model from the issue text.