Migrate docs into Forest repo

[ansermino]

Summary

The plan is to move the Forest docs currently in chainsafe/forest-docs-v2 into this repo.

Completion Criteria

• Remove push access to forest-docs-v2
• Add new docs to forest under /docs
• Reconfigre GHA for linting, PR previews and deployments
  • Merge Makefiles
  • Update dependabot config
  • Add lint and check pipeline
  • Add deployment pipeline
  • Scope GHA to only run on relevant files
• Update README for docs
• Migrate relevant issues from forest-docs-v2 to forest
• Deprecate forest-docs-v2
• Migrate docs from /documentation into the new developer docs
• Remove /documentation

Additional Links & Resources

[LesnyRumcajs]

note: we should remember to adjust/verify GH projects, there might be some automation in place.