Add Heroku add-on

[hoangmirs]

Why

We often deploy the project to Heroku by default. But we still need to add some extra steps to create the Heroku app, add the database add-ons, set some default environment variables. Therefore, we should add the Heroku add-on to generate the Terraform code and guideline to make the deployment faster

Insights

It was implemented in recruitmate-web:

• https://github.com/nimblehq/recruitmate-web/pull/10
• https://github.com/nimblehq/recruitmate-web/pull/25