Use Document[] for aggregation pipeline types in MessagesRaw

Description
In MessagesRaw.ts, the aggregation pipeline stages are typed using a brittle workaround:

Expected Behavior
Pipeline stages should be typed as Document[] which is the correct type from the MongoDB driver and is already imported in the file.

Current Behavior
const match = { $match: { ... } };
const lookup = { $lookup: { ... } };
const unwind = { $unwind: { ... } };
const group = { $group: { ... } };
const project = { $project: { ... } };
const firstParams: Exclude<Parameters<Collection<IMessage>['aggregate']>[0], undefined> = [match, lookup, unwind];
const sort = { $sort: options.sort || { name: 1 } };
const params = [...firstParams, group, project, sort];
const query = { 'u._id': userId, '$or': [{ 'file._id': { $exists: true } }, { 'files._id': { $exists: true } }], };
const update = { $set: { _hidden: hidden, },};

Steps to Reproduce
See packages/models/src/models/Messages.ts

Additional Context

• Document is already imported from mongodb and IMessage is already imported from @rocket.chat/core-typings
• No runtime behavior changes, types only
• Resolves the existing // FIXME: aggregation type definitions comment
• The following variables should be typed as Document:
  • match
  • lookup
  • unwind
  • group
  • project
  • sort
• The following arrays should be typed as Document[]:
  • firstParams
  • params
• The following object should be typed as Filter<IMessage>:
  • query
• The following object should be typed as UpdateFilter<IMessage>:
  • update

Open packages/models/src/models/Messages.ts and locate the FIXME about aggregation type definitions and the MessagesRaw implementation. Read the existing mongodb imports and the aggregation setup, then apply the requested Document, Document[], Filter, and UpdateFilter annotations to the named variables. Done means the brittle workaround is removed without runtime changes and the file's type checks pass.