🔥Docker and environment variables cleanup (#270)

* Added dotenv-rails gem to manage environment variables

* Added dotenv-rails gem to manage environment variables
* Removed figaro which was used earlier for this purpose

* Standardized variable names

* Changed all env variables to be upper case. This included changes in files referencing env variables.
* Added example env file with all variables set to empty value
* Removed the earlier setup of copying application.yml and database.yml and the scripts and documentation associated to this

* Docker setup

* Added docker file for building the docker images
* Added entrypoint.sh script which is referenced inside the Docker image
* Cloned the Procfile for development using docker which has slight change compared to regular procfile
* Added the docker-compose.yml which has 3 service's configuration, postgres, redis and chatwoot server and a mounted volume for postgres

* Added docker related info to documentation

* Added the docker setup info in the documentation
* Added info for using`rbenv` instead of rvm for managing ruby versions
* Updated the documentation for environment variables to have one about `dotenv-rails` gem and removed the documentation about the old copy paste method used by figaro

* Changing the postgres database, username and password as environment variables

* Removed database.yml from gitignore
* Made the postgres databse, username and password as environemnt variables
* Added this in documentation

* Added a quick setup page

* Added quick setup page
* Removed the docs from README and added link to the docs in website
* Removed the figaro related things from circle.ci config

* Adding external volume for redis in docker compose

* Added instructions for adding the redis volume in docs

Gemfile.lock

@@ -191,6 +191,10 @@ GEM
     diff-lcs (1.3)
     domain_name (0.5.20190701)
       unf (>= 0.0.5, < 1.0.0)
+    dotenv (2.7.5)
+    dotenv-rails (2.7.5)
+      dotenv (= 2.7.5)
+      railties (>= 3.2, < 6.1)
     equalizer (0.0.11)
     erubi (1.9.0)
     execjs (2.7.0)
@@ -207,8 +211,6 @@ GEM
     faraday (0.17.0)
       multipart-post (>= 1.2, < 3)
     ffi (1.11.1)
-    figaro (1.1.1)
-      thor (~> 0.14)
     foreman (0.86.0)
     globalid (0.4.2)
       activesupport (>= 4.2.0)
@@ -462,10 +464,10 @@ DEPENDENCIES
   chargebee (~> 2)
   devise!
   devise_token_auth!
+  dotenv-rails
   facebook-messenger
   factory_bot_rails
   faker
-  figaro
   foreman
   haikunator
   hashie