graphql-http, rewrites, redirects, explorer plugin

[acao]

• replace express with graphql-http, lambda handler
• add netlify-cli tooling to simplify npm run watch
• add reverse proxy from .netlify/functions/graphql to /graphql so that /graphql serves a graphql schema, for a relative /graphql path as is an ad-hoc and familiar standard
• add 301 redirects so that ./netlify/functions/index and ./netlify/functions/swapi permanently redirect to /graphql
• lint:fix
• configure CORS at netlify gateway level
• add explorer plugin

result:

• https://graphql.org/swapi-graphql/graphql will be usable as a graphql schema
• previous function urls rewrite and/or redirect to this /graphql schema path
• use the spec reference implementation
  • graphiql explorer plugin as a treat