Setup GitHub Actions workflow for formatting, linting, and typechecking

[RishikeshNK]

Please see .github/workflows/main.yml:

env:
  NODE_VERSION: 20
  PNPM_VERSION: 8

  # Find a workaround to this.
  DATABASE_URL: "postgresql://admin:admin@localhost:5432/cooper?schema=public"
  NEXTAUTH_URL: "localhost:3000"

This is a temporary workaround since the linting script, I believe, runs the files. The src/env.js file is responsible for type-checking the environment files. For now, I have added non-production environment variables to the workflow file. I will create a new pull request once I figure out a workaround to this in the future.