🔧 chore[Jenkinsfile]: streamline environment setup and improve branch…

[boytur]

This pull request includes significant updates to the Jenkinsfile to improve the CI/CD pipeline's efficiency and clarity. The changes focus on restructuring the pipeline stages, enhancing environment setup, and simplifying the notification mechanism.

Environment Setup and Variable Handling:

• Introduced a new Determine Environment stage to set environment variables based on the branch name.
• Added a Setup .env stage to load environment-specific files securely.

Stage Renaming and Simplification:

• Renamed stages for clarity: Setup Environment to Setup Environment Variables, Checkout & Pulling to Checkout & Pull, Testing with Jest to Run Tests, and Docker Build & Deploy to Build & Deploy Docker. [1] [2]

Notification and Post Actions:

• Simplified the Slack notification message in the post section to include only essential information.

These changes streamline the pipeline, making it more maintainable and easier to understand.