Part of #76140

This will consolidate all the scheduler configs into one yaml based config.

Repos to Migrate

• Migrate flutter/cocoon - [scheduler] ci migration script cocoon#1202
• Migrate flutter/flutter - Migrate to .ci.yaml #82960
• Add Cocoon .ci.yaml check - [scheduler] ci.yaml check run cocoon#1229
• Remove linux_validate_ci builder - https://github.com/flutter/infra/pull/460
• Migrate flutter/engine - Migrate to ci.yaml engine#26271
• Migrate flutter/packages - Migrate to .ci.yaml packages#361
• Migrate flutter/plugins - Migrate to .ci.yaml plugins#3938
• Add all ci yaml files to cocoon integration test - [scheduler] Add all repos with ci.yaml to integration test cocoon#1227
• Remove "validate_json" step - https://flutter-review.googlesource.com/c/recipes/+/13641