Move conftest so we can use testr

[jzuhone]

Description

Attempting to run the dpa_check regression tests from the ska3 flight repository results in an error:

import dpa_check
dpa_check.test()

...  many errors like this:

____________________ ERROR at setup of test_JUL3018A_viols _____________________
file /Users/aldcroft/miniconda3/envs/ska3/lib/python3.8/site-packages/dpa_check/tests/test_dpa_viols.py, line 7
  def test_JUL3018A_viols(answer_store, test_root):
E       fixture 'answer_store' not found
>       available fixtures: capfd, capfdbinary, caplog, capsys, capsysbinary, doctest_namespace, monkeypatch, pytestconfig, record_property, record_testsuite_property, record_xml_attribute, recwarn, tmp_path, tmp_path_factory, tmpdir, tmpdir_factory
>       use 'pytest --fixtures [testpath]' for help on them.

This PR moves the conftest.py file to the actual package so it gets copied over in the install.

Testing

• Passes unit tests on MacOS, linux, Windows (at least one required)