IER12 Feedback Error Types

**Current Behaviour**
SIMS is using hardcoded Ecert Feedback Errors to determine `applicationEventDate`.

**Expected Behaviour**
SIMS should dynamically use Ecert Feedback Errors from the current table to determine `applicationEventDate`.

**Acceptance Criteria**
- [ ] IER12 process should remove hardcoded error codes and instead, refer to the `ecert_feedback_errors` for error codes

Start by locating the IER12 process and the code that currently uses hardcoded Ecert Feedback Errors to determine applicationEventDate. Read how the ecert_feedback_errors table is represented and queried; done means IER12 derives the date using the current table's error codes rather than hardcoded values.

Written by the indexing model from the issue text.