Set up an 2 API endpoints for new "missions" generation.

[hoanghm]

• [x] Make sure outputs are json-parsable (Can split this into 2 steps: 1. Generate task --> 2. Format task to JSON)
• [x] Add an API endpoints for weekly mission generation

• [x] Add an API endpoint for ongoing mission generation

  • Endpoints format:

    "// Input"
    {
    "user_id":  "str", 
    "num_missions": "int" 
    }
    
    "// Output"
    {
    "new_missions": [
      {
        "id": "...",
        "title": "...",
        "description": "..."
        "steps": "..."
      },
    ]
    }

[hoanghm]

Added 2 endpoints:

• GET /get_weekly_missions/<user_id>/<num_missions>
• GET /get_ongoing_missions/<user_id>/<num_missions>

Both return responses of the format

{
     "new_missions": [
         {
           "id": "...",
           "title": "...",
           "description": "..."
           "steps": "..."
         },
         // ... there can be multiple missions generated
     ]
   }

[ogallagher]

We may not use these endpoints if frontend directly queries the firestore db.