Update Technology Recommendations and Related Decisions

[feanil]

While creating OEP-67 we got a lot more eyes on the current Frontend recommendations than we had in a while. As a result we found some recommendations that need to be reviewed and potentially updated.

Updates to existing recommendations

• OEP-67 - Greenkeeper is an out-of-date recommendation #524
• Redux may no longer be recommened, review and update OEP-67 recommendation.
• Codecov is generally recommended not just recommended for the frontend, add a new overall ADR to reflect this general recommendation.

Historic Standards that need notes and ADRs

• Django
• DRF
• drf-yasg
• tox
• pytest
• edx-lint