feat: configurable labels

[vigneshrajsb]

What

• removes fastly purge cache label
• uses config to set default labels to deploy, destroy and status comment
• config to enable status comments by default. eg orgs with no UI

Testing

auto_deploy:
- create PR, add label ✅
- close PR, remove label ✅
- default status comment = true, add status comment ✅
- default status comment = false, no status comment ✅
- default status comment = false, no status comment, add custom label to get status comment ✅
---


non auto deploy:
- create PR, add label ✅
- close PR, remove label ✅
- default status comment = true, add status comment ✅
- default status comment = false, no status comment ✅
- default status comment = false, no status comment, add custom label to get status comment ✅
---
- disabled label with deploy ✅
- disable label removing deploy ✅

missing config for labels
- create PR, add label ⏳, deploy PR ✅
- close PR, remove label ⏳ ✅

[vmelikyan]

This is a great addition, thank you @vigneshrajsb