[Improvement] remove the restriction for custom policy type

### What would you like to be improved?

We could only create one custom policy type

### How should we improve?

remove the restriction for custom policy type to support more type like `custom-ttl`, `custom-compaction`

No files, tests, or entry points are named in the issue; begin by locating the code that enforces the single custom policy type restriction and its existing tests. Done means creation accepts multiple custom policy types, including `custom-ttl` and `custom-compaction`, with coverage for the supported types.

Written by the indexing model from the issue text.