Add support for LDAPS testing

[cdprete]

Hello.

I tried to ask for this feature in spring-projects/spring-data-ldap#588 and @mp911de redirected me here. :)

Copied from the ticket:

The InMemoryDirectoryServer created in org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration supports only an LDAP connection, but the InMemoryListenerConfig used in there can be created easily for both.

The suggestion in this ticket is to extend the spring.ldap.embedded properties to allow to specify a server and, eventually, a client SslBundle name to use to create the InMemoryListenerConfig with SSL.