add `engines` to clarify the minimum nodejs version

[micalevisk]

for better DX on using this package, I'd suggest you to add the following to package.json:

  "engines": {
    "node": ">=18"
  },

as of now the flat dependency has it and so we know that we must use nodejs 18+ if we want to use @baselime/node-opentelemetry but I think that it would be better if @baselime/node-opentelemetry itself dictates that instead of relying on their deps