Admin API Route: /policies/attachments

This policy will control the size and file types of attachments.

• id: policy ID, previous revisions retrievable by GET /policies/attachments/:id
• allowed_types: map of allowed MIME types (globbing is allowed) to maximum sizes in octets, if a key has a null size, it follows the general maximum size
• denied_types: list of denied MIME types (globbing is allowed)
• whitelist: if true, everything except allowed_types are denied, and denied_types are subtracted from allowed_types; else, everything except denied_types are allowed, and allowed_types are subtracted from denied_types
• cdn_endpoint: fully qualified domain name plus path to the CDN endpoint
• size: maximum size in octets

Sub-tasks:

• Retrieve single: GET /policies/attachments/:id
• Retrieve all: GET /policies/attachments
• Create: POST /policies/attachments/:id
• Update single: PATCH /policies/attachments/:id
• Atomic swap: TRANSPOSE /policies/attachment/:id /policies/attachment/:id
• Remove single: DELETE /policies/attachments/:id

Start by reviewing the listed admin API routes and the attachment policy fields in this issue, including the revision, filtering, and atomic-swap requirements. Done means implementing and verifying retrieval, creation, update, swap, and deletion for the attachment policy endpoints, with the documented path and field behavior.