feat: Implement python-decouple for environment variables management

[smkbarbosa]

This pull request introduces the use of python-decouple to manage the environment variables of the Django-CRM project. It also updates the installation and configuration documentation to reflect this change.

Motivation:

• Security: Storing sensitive information (such as API keys, database credentials) outside the source code, in a .env file, increases the security of the project.

• Flexibility: Makes it easier to configure the project in different environments (development, testing, production) without changing the code.

• Organization: Centralizes the configurations in a .env file, making management simpler and more organized.

• Consistency: Ensures that environment variables are loaded consistently across all environments.

Change Details:

1. Installation of python-decouple:

• Added python-decouple to requirements.txt.
• Instructions for installing dependencies have been updated in the documentation.

2. Creation of the .env File:

• Added a sample .env file (contrib/env-sample) to serve as a template.
• Instructions for creating and configuring the .env file have been added to the documentation.

3. Modification of settings.py:

• The webcrm/settings.py file has been updated to use python-decouple to read environment variables.
• Examples of how to use config() have been added to the documentation.

4. .gitignore:

• Added .env to .gitignore to prevent sensitive information from being sent to the repository.

5. Documentation:

• The "Settings of Django CRM" section has been updated with a new subsection "Environment Variables and python-decouple".
• Detailed instructions on how to set environment variables have been added.
• Explanations on the benefits of using environment variables have been included.
• Information on how to use dj-database-url has been added to make database configuration easier.

Impact:

• The project is now more secure, since sensitive information is no longer in the code.
• The project configuration is more flexible and organized.
• It makes it easier for new developers to contribute to the project.

Testing:

Local testing has been performed to ensure that the project works correctly with the new settings.

• The documentation has been revised for clarity and accuracy.

Checklist:

• python-decouple installed and configured.
• .env file created and configured.
• settings.py updated to use python-decouple.
• .env added to .gitignore.
• Documentation updated.
• Local testing performed.
• dj-database-url installed and configured.