WIP: mongodb connector

[doodlesbykumbi]

What does this PR do?

• What's changed? Why were these changes made?
• How should the reviewer approach this PR, especially if manual tests are required?
• Are there relevant screenshots you can add to the PR description?

What ticket does this PR close?

Connected to #260

Checklists

Change log

• [ ] The CHANGELOG has been updated, or
• [ ] This PR does not include user-facing changes and doesn't require a CHANGELOG update

Test coverage

• [ ] This PR includes new unit and integration tests to go with the code changes, or
• [ ] The changes in this PR do not require tests

Documentation

• [ ] This PR does not require updating any documentation, or
• [ ] Docs (e.g. READMEs) were updated in this PR, and/or there is a follow-on issue to update docs

(For releases only) Manual tests

• [ ] Manually tested Keychain provider
• [ ] Manually run Kubernetes-Conjur demo with a local Secretless Broker image build of your branch