Add Connect API Code

[rjwignar]

Adds Connect API example code from https://github.com/canva-sdks/canva-connect-api-starter-kit.
Requires a .env file in connect-api\demos\ecommerce_shop:

BACKEND_PORT=3001
BACKEND_URL=http://127.0.0.1:3001
FRONTEND_URL=http://127.0.0.1:3000
BASE_CANVA_CONNECT_API_URL=https://api.canva.com/rest
CANVA_CLIENT_ID="<CANVA_CLIENT_ID>"
CANVA_CLIENT_SECRET="<CANVA_CLIENT_SECRET>"
# See README for how to generate this
DATABASE_ENCRYPTION_KEY="<DATABASE_ENCRYPTION_KEY>"

To run, first navigate to the repository root then run the following commands:

cd connect-api
npm install
cd demos/ecommerce_shop
npm install
npm start