feat(rest): add policy management APIs

[plusplusjiajia]

Purpose

Ports the data-policy half of the experimental REST management API added in apache/paimon#9400 to Rust: the row filters and column masks a REST catalog stores per principal and applies at read time.

What it adds

GET  /v1/{prefix}/databases/{db}/tables/{table}/policies?type&principal&column&maxResults&pageToken
POST /v1/{prefix}/databases/{db}/tables/{table}/policies
POST /v1/{prefix}/databases/{db}/tables/{table}/policies/drop

api/management.rs gains PolicyType, RowFilter, ColumnMask, DataPolicy and ListPoliciesRequest, mirroring org.apache.paimon.management, and RESTApi gains list_policies, create_policy and drop_policy, with thin delegates on RESTCatalog. Wire names, query parameters and client-side validation follow Java. No new dependencies.