feat: revert backwards-incompatible changes for v5.14.0 (#2169)

* Revert "refactor: simplify isUenValid logic (#2156)"

This reverts commit 8f0eda6.

* Revert "feat: add UEN field (#2100)"

This reverts commit 35eeeaf.

* Revert "feat: add and call v3 API for retrieving individual admin form (#2113)"

This reverts commit e55e1a9.

* Revert "chore: remove redundant ValidationOption object properties for short text, long text and number fields (#2040)"

This reverts commit 95b6297.

* Revert "feat: Add webhook support for storage mode attachments (#1713)"

This reverts commit 332d3ce.