feat: add environment secrets support [sc-21028]

[maxigimenez]

I hereby confirm that I followed the code guidelines found at engineering guidelines

Affected Components

• [x] CLI
• [ ] Create CLI
• [ ] Test
• [ ] Docs
• [ ] Examples
• [ ] Other

Notes for the Reviewer

• [x] Add --secret support while creating/updating environment variables with npx checkly env add|update
• [x] Add secret: boolean support for check/group constructs
• [x] Update npx checkly env pull to structure the file with regular and secret variables

[!IMPORTANT] Important note: this feature is not available yet, if you have any questions feel free to reach out to our customer support

[github-actions[bot]]

🎉 Experimental release successfully published on npm

npm install checkly@0.0.0-pr.964.1aa6287

[Antoine-C]

Reviewing 👀