[Projects] Add Get Project Expenditures Route (GET /projects/{id}/expenditures)

[nourshoreibah]

User Story

As a user I want to view all expenditures for a project so that I can track spending.

Description

• Add GET route to projects Lambda.
  Command:
  node tools/lambda-cli.js add-route projects GET /projects/{id}/expenditures
• Join proj_expend with expenditures using projectID.
• Return expenditure list.

Acceptance Criteria

• Returns 200 with expenditures array.
• Returns empty array if none exist.