Update docker-compose.yml to handle authenticators

[szjarek]

Ensure that CONJUR_AUTHENTICATORS environment variable is passed to the conjur container. This is required to handle multiple authenticators when using docker.

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?

Resolves #[relevant GitHub issues, eg 76]

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

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

[izgeri]

Hey @szjarek - thanks for submitting this. It looks like a reasonable change, but before I approve can you please make sure you've read and understood our contributor agreements? In particular, to accept this contribution I will need you to either amend your commit to include your signoff or for you to sign the contributor agreement. The link I shared has specific instructions for how to amend your git commit - that's the easiest way to move forward.

Thank you! If you have any questions, feel free to ask here or on discourse.

[szjarek]

Hi @izgeri, thank you for your attention! I've some issues with amending this change and didn't want to push a "messy" commit, so I've created another pull request - this time (hopefully) with a proper signoff included. Thanks!