rptest: use okta auth for teleport

[andrewhsu]

without this fix, will get error:

ERROR: no github connectors found

validated fix with test:

ducktape \
  --debug \
  --globals=/home/ubuntu/redpanda/tests/globals.json \
  --cluster=ducktape.cluster.json.JsonCluster \
  --cluster-file=/home/ubuntu/redpanda/tests/cluster.json \
  tests/rptest/tests/services_self_test.py::SimpleSelfTest.test_cloud

output:

test_id:    rptest.tests.services_self_test.SimpleSelfTest.test_cloud
status:     PASS
run time:   54.454 seconds
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
========================================================================================================================================================================================
SESSION REPORT (ALL TESTS)
ducktape version: 0.8.18
session_id:       2024-02-06--004
run time:         54.472 seconds
tests run:        1
passed:           1
flaky:            0
failed:           0
ignored:          0
opassed:          0
ofailed:          0
========================================================================================================================================================================================

Backports Required

• none - not a bug fix
• none - this is a backport
• none - issue does not exist in previous branches
• none - papercut/not impactful enough to backport
• v23.3.x
• v23.2.x
• v23.1.x

Release Notes

• none