feat(ci): add PR automation with labeling and assignment

[rahul810050]

Description

This PR adds GitHub Actions automation to streamline PR management by automatically labeling, sizing, and assigning reviewers to pull requests.

Changes Made

• Added PR labeling workflow based on file changes
• Implemented size labeling (XS, S, M, L, XL) based on lines changed
• Configured auto-assign for reviewers based on expertise
• Added welcome message for first-time contributors

Key Features

Auto-labeling

• api - Changes in src/api/
• components - Changes in src/components/
• pages - Changes in src/pages/
• dependencies - Changes in package.json
• documentation - Changes in .md files
• tests - Changes in test files

Size Labels

• XS: < 10 lines
• S: 10-30 lines
• M: 30-100 lines
• L: 100-500 lines
• XL: > 500 lines

Auto-assign

• Automatically assigns relevant reviewers based on file changes
• First-time contributors get a welcome comment

Files Added

• .github/workflows/pr-automation.yml - Main workflow
• .github/labeler-config.yml - Labeling rules
• .github/auto-assign.yml - Reviewer assignment

Testing

• Verified labels are added correctly
• Confirmed size calculation works
• Tested auto-assign with different file types
• Validated first-time contributor message

Benefits

• ⏱️ Reduces manual PR triage time
• 🏷️ Ensures consistent labeling
• 👥 Faster reviewer assignment
• 🚀 Better contributor experience

Fixed issue: #324