Improve Gmail API auth, refactor email extraction, and limit email fetch to 3

[poulami-mukherjee]

Improve Gmail API authorization, refactor email extraction logic, and rebased from latest changes:

• Implemented handling for UserRecoverableAuthIOException to request user consent for Gmail API access.
• Refactored extractEmailContent and extractRecommendedActions for better structure and efficiency.
• Replaced hardcoded sensitive debug keystore credentials with environment variables for security.
• Updated .gitignore to exclude more generated and unnecessary files from version control.
• Modified Gradle build to support user-specific signing configurations and set minSdk to 26.
• Limited number of Emails fetched to 3 from 10
• Rebased from latest changes and minor code refactor