[Feature] Ldap auth support

### Relevant component

refarch-gateway

### Problem description (optional)

Currently only oAuth2 can be used for authentication in the gateway and JWT is used for authentication for services behind the gateway.

### Desired solution

As some of the open source RefArch applications are interesting for reusing in other municipalities/companies and not everyone of them uses a Keycloak for authentication the possibility to do the authentication and authorization via LDAP should be introduced.
For the DAVe Project this usecase was already externally requested.
Things to think about:
- Authorization: Roles/permissions via ldap-groups?
- Authentication between Gateway and Services
- Easy maintanability
- The alternatives could be more practical

Indirectly might require https://github.com/it-at-m/refarch-templates/issues/354 and https://github.com/it-at-m/refarch-templates/issues/258 as prerequisite.

### Considered alternatives (optional)

- Integrate LDAP into Keycloak: https://www.keycloak.org/docs/latest/server_admin/#adding-a-provider

### Additional context (optional)

- DAVe Issue: https://github.com/it-at-m/dave-backend/issues/80
- Internal tracking issue: https://git.muenchen.de/ccse/auftragsmanagement/einsaetze/-/issues/443

### No duplicate

- [X] I confirm that this issue is not a duplicate

### Code of Conduct

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