PostgreSqlFlexibleServerVersion enum missing Ver16, PostgreSQL 16

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Is your feature request related to a problem? Please describe the problem.

I have an existing project that I currently deploy via the `azd` tool, that I would like to migrate to Aspire. However, the `PostgreSqlFlexibleServerVersion` enum doesn't currently have an entry for PostgreSQL 16, the version I'm currently using.

### Describe the solution you'd like

I would like to see support added for PostgreSQL 16 in the Azure PostgreSQL Flexible Server tooling.

### Additional context

_No response_