feat: add include filter support to the GET /api/v3/proposals endpoint

[jekabs-karklins]

Description

Add include filter support to the GET /api/v3/proposals endpoint, allowing callers to request associated samples inline within a single query.

Motivation

The proposals endpoint only supported simple find() queries with no relation expansion. We used to need to make separate requests to fetch samples belonging to a proposal. The dataset endpoint already supports this pattern via MongoDB aggregation $lookup stages - this change brings proposals to parity.

The following query now works

curl -X 'GET' \
  '<backend>/api/v3/proposals' \
  -H 'Authorization: Bearer <token>' \
  -H 'accept: application/json' \
  --data-urlencode 'filter={"where":{"proposalId":"123456"},"include":[{"relation":"samples"}]}'

Fixes

SWAP-5421

Changes:

• Added src/proposals/types/proposal-lookup.ts — defines ProposalLookupKeysEnum and PROPOSAL_LOOKUP_FIELDS with a $lookup stage joining Sample on Sample.proposalId = Proposal.proposalId
• Added src/proposals/interfaces/proposal-relations.interface.ts — IProposalFilters, IProposalRelation, IProposalScopes types mirroring the dataset filter interface pattern
• Added findAllComplete(), addLookupFields(), and extractRelationsAndScopes() to ProposalsService — builds an aggregation pipeline with optional $lookup stages and applies scope-level where, fields, limits
• Updated GET /proposals in ProposalsController — routes to findAllComplete() when include is present in the filter, otherwise falls back to existing findAll()
• Updated IncludeValidationPipe — extended the strict union type to include ProposalLookupKeysEnum alongside the existing dataset and origdatablock enum types

Tests included

• Included for each change/fix?
• Passing?