Migrate to LDAP-module v2

[tvdijen]

Depends on https://github.com/simplesamlphp/simplesamlphp-module-ldap/pull/37 to be merged and released into v2.1

Updates the module to use the new major version of the LDAP-module. Drops the requirement to set all the ldap-connection details in the negotiate-authsource. Instead the backend-authsource is used. The fallback-authsource can now also be a non-ldap source (backend and fallback are now differentiated).

[codecov[bot]]

Codecov Report

Merging #5 (ef8e97e) into master (a92cac1) will increase coverage by 3.44%. The diff coverage is 0.00%.

:exclamation: Current head ef8e97e differs from pull request most recent head 26fa964. Consider uploading reports for the commit 26fa964 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #5 +/- ## ============================================ + Coverage 26.66% 30.10% +3.44% + Complexity 57 54 -3 ============================================ Files 2 2 Lines 210 186 -24 ============================================ Hits 56 56 + Misses 154 130 -24 ```

[tvdijen]

Tested & works like a charm in different scenarios:

• Kerberos remains in working condition
• Fallback to LDAP-backend works
• Fallback to some third party authsource works

Once approved, I will make the exact same changes to the negotiate-ext module