Split apart e2e tests for the different sources

[tlater-famedly]

          I added a test that combines LDAP and UKT syncing into one as per your suggestion. Also, as per your suggestion in another comment, let's postpone the division of tests for another PR.

Originally posted by @jannden in #49 (comment)

This would be nice to do before we start adding more sources, as the e2e test file will just keep growing if we don't get to this.

In addition, we should see if using nextest's test group feature makes sense here, since the non-ldap tests would not need an LDAP server to run, so if a specific subset of tests is run we could save ourselves the effort of spinning that up.