(back) add oaipmh service for corpora

The OAI-PMH service notably doesn't limit the answer size, and thus
doesn't reply with partial answers and resumptionTokens - yet.
3 jobs for oaipmh in 11 minutes and 39 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build
passed build #474715

00:03:03

 
  Test
failed back #474716

00:08:36

passed front #474717

00:02:49

 
Name Stage Failure
failed
back Test
  File "/builds/synalp/olki/olki/olki_back/.tox/py37/lib/python3.7/site-packages/environ/environ.py", line 277, in get_value
raise ImproperlyConfigured(error_msg)
django.core.exceptions.ImproperlyConfigured: Set the AUTH_LDAP_ENABLE environment variable
ERROR: InvocationError for command /root/.poetry/bin/poetry run pytest (exited with code 1)
___________________________________ summary ____________________________________
ERROR: py37: commands failed
Makefile:67: recipe for target 'test-be' failed
make: *** [test-be] Error 1
ERROR: Job failed: exit code 1