Explore retaining high-volume responses within GC Forms

### Description:

As part of the high-volume response pilot, explore whether we could support higher-volume use cases by retaining responses within GC Forms, rather than building a mechanism to move or remove high-volume response data from GC Forms.

This could also consider how this approach might connect with the CRM CDS is building and whether it could help us manage or track work related to these clients.

#### Need to explore policy implications:
- [ ] Security/privacy risks of retaining responses longer-term
- [ ] CDS’s overall comfort with holding this data long-term
- [ ] Any retention, storage, or policy constraints we would need to account for

No files, tests, or entry points are named. Start by mapping how GC Forms currently handles high-volume responses, then investigate long-term retention, storage, security/privacy, policy constraints, and how the approach could connect with CDS’s CRM. Done means a documented feasibility assessment and a clear decision or recommendation.

Written by the indexing model from the issue text.