switch to monorepo: second phase

[MartijnR]

• merge latest from enketo/enketo
• add final code changes to enketo-express-oc (i.e. changes after December 1st)
• move issues to new repo
• archive enketo-express-oc after point to new repo enketo-express-oc#752 has been merged
• move all enketo-core function overwrites into enketo-core directly for easier maintenance - skipped some
• move 2 added strings in translation.json to translation-additions?
• do final diff check with enketo/enketo after the previous point to see if there are any remnant customizations that are no longer required or could be refactored

consider to also include:

• move custom XPath functions that OC has added from its own repo to this monorepo (not as a separate package) - move to enketo-oc enketo-xpath-extensions-oc#26 - best to hold off until necessary to change
• rename all files that OC has added to include the -oc postfix

[MartijnR]

moved open issues, using github client, with:

gh issue list -L 500 --json number | \
  jq -r '.[] | .number' | \
  xargs -I% gh issue transfer % https://github.com/OpenClinica/enketo-oc.git

Apologies for all the emails if you were subscribed to the issues... I'm glad we only did the open issues...

[MartijnR]

The good news is that the issues have kept their labels and milestones (because I copied those in advance). However, the ordering of issues within the milestone is lost.