Make a CURL upload to Bookworm with a DEP-8 test to address LDAP issues.

I discussed this with Samuel on IRC. A lot of LDAP behavior is broken and relies on deprecated interfaces due to this Autotools bug in CURL, where it doesn't take advantage of OpenLDAP-specific functionality. To meet a high standard of proof that this is appropriate for Bookworm, I wrote an autopkgtest that spins up a real instance of slapd the LDAP server and verifies that a critical quirk is fixed.

Most importantly, the autopkgtest can be verified to fail without the patch, and pass with. The test is appropriate for inclusion into the Unstable package presumably without change (but I concede I haven't verified this yet).