Improve contributing experience

[hyperupcall]

• [BREAKING]: Use Node 18 for CI and minimum required engines parameter
  • Nodejs v16 EOL's (security patches) in ~1 month
  • Nodejs v18 is the first version that includes the node:readline/promises module (that this PR uses)
• Significantly improves organization and instructions in CONTRIBUTING.md
• README.md Grammar improvements
• Adds new_schema Grunt task for making it easier to create a new schema
• Adds linting Grunt tasks
• Adds a local schema for schema-validation.json
• Adds npm scripts for Prettier and name the scripts to what's more in line with the npm ecosystem (keep old names for compatibility with existing workflows)

Closes #3107

[madskristensen]

This is an excellent improvement. There appear to be merge conflicts, though

[madskristensen]

Thanks!!