Revert sequelize update to v6 changes

revert "fix(deps): update dependency sequelize to v6 [security]"

This reverts commit c625e5dad7a1ad81b0d17d8b80cc6e00fd560a34.

use snake_case instead of camelCase with updateOnDuplicate

v1.3.17

More debug logging

Increase debug logging

v1.3.16

More debug logging

Remove erroneous unique: true, debug logging

v1.3.15

Remove misleading unique: true from studyrights model, add debug cons…

Fix incorrect promise handling caused by Sequelize major update

v1.3.14

Avoid chaining filter/map directly to sequelize model to bugs caused …

Fix `/grapa/studytracks` API, add `code` field to the response body

v1.3.13

Fix lint issue

add endpoint GET grapa/studytracks/:code

v1.3.12

fix formatting

Security dependency updates

v1.3.11

Merge pull request #233 from UniversityOfHelsinkiCS/renovate/npm-expr…

Add /persons endpoint for the new Grapa service

v1.3.10

Fix lint errors

Remove requestBuffer

Removing requestBuffer to reduce complexity of the system and avoid sneaky bugs in the future.
This at the same time fixes an issue where on failure and retry, importer does not flush requestBuffer (bug introduced in this PR), which means it fetched the next page on retry instead of retrying the same page. This bug resulted in missing data across multiple data types