DBIO: tweak search API

[RayPlante]

The is PR is in response to a review of the feature/dbio-selected-ep branch which introduces advance query capabilities based around the MongoDB filter query syntax. In particular, it recommends the following changes:

• change function name, select_constraint_records() to adv_select_records() for clarity
• change signature for select_records() to allow for arbitrary keyword-value constraints to allow for future simple shortcut queries (e.g. author=Plante or keywords=forensics).
• limit the available MongoDB operators via check_query_structure()

Unit tests have been updated to adapt to the API changes.

Please test in two ways

• ensure that the unit tests pass; in this branch:
  1. run scripts/testall.pyunit (make sure MONGO_TESTDB_URL is not set)
  2. run the test_mongo.py script:
     1. Start the midas server stand-alone: scripts/midasserver -b -M
     2. set the MONGO_TESTDB_URL environment variable: export MONGO_TESTDB_URL=mongodb://oarop:oarop@localhost:27017/midas
     3. ensure your PYTHONPATH is properly set (export PYTHONPATH=$PWD/dist/pdr/lib/python) and dependencies are installed.
     4. run the test script: python python/tests/nistoar/midas/dbio/test_mongo.py
• test under oar-docker:
  1. Check out the feature/dbio-mongo branch of oar-docker
  2. Change into the oar-docker/midas directory
  3. Build all components: ../scripts/localdeploy
  4. Build all containers: ../scripts/oarctl local build
  5. Launch application: ../scripts/oarctl local up
  6. Use portal to send advance queries to the DBIO service.