ci: create pages workflow

[vladimirleonidovich]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/docs.nestjs.com/blob/master/CONTRIBUTING.md

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Docs
• Other... Please describe: CI/CD

What is the current behavior?

Some countries block access to https://docs.nestjs.com/ and users from these countries cannot access the documentation.

What is the new behavior?

Publishes documentation on GitHub Pages so that users can access from countries where https://docs.nestjs.com/graphql/ is blocked.

Does this PR introduce a breaking change?

• Yes
• No

Other information

Enable deployment of GitHub Pages from GitHub Actions before merging.

[kamilmysliwiec]

Please, report this issue to Netlify then