Added postgres port env variable

[antoineludeau]

Context

In order to make a progressive infrastructure evolution of the postgresDB, We need to be able to set the postgresql db access port easily.

Enhancement

This PR adds the possibility to set the postgresql port through an env variable :

• POSTGRES_PORT = ... (the desired port)

TO-DO before going to production

• add a POSTGRES_PORT env variable to the .env file in production (it will work without it because we have set a default value in the code if the variable is empty).