#161966905 Configure Authors Haven to use PostgreSQL as DB Engine

[PromasterGuru]

What does this PR do?

• Configure Authors Haven to use PostgreSQL as DB Engine

Description of Task to be completed?

• Install the PostgreSQL database and update Authors Haven to use it.

Any background context you want to provide?

• PostgreSQL is Open Source, fully featured and optimized for production-ready environments as compared to SQLite that comes as default with the Authors Haven application.

What are the relevant pivotal tracker stories?

#161966905

Screenshots (if appropriate)

[r-wambui]

I have merged the previous PR, kindly rebase develop so that we can have only changes related to this PR. Remember to solve also the merge conflicts

[r-wambui]

Please add database configuration to the readme as well. In this case any user of the app will be able to set up postgres.

[kamyaD]

The configuration works perfectly, I have run migration and proved that PostgreSQL works