chore: change error handler to use logger.error

[alexanderleegs]

Problem

Resolves ISOM-916. Previously, our catch-all error handler was using logger.info, which meant that unrecognised/unhandled errors were being tagged as info in datadog. This PR modifies them to use logger.error instead.

Tests

• [ ] Visit the workspace of a-test-v4 (https://staging-cms.isomer.gov.sg/sites/a-test-v4/workspace)
• [ ] Click on the YAML error page, which should bring you to an error page
• [ ] Verify on DD that the error message is logged as an error