let settings.httpNodeAuth accept single middleware or array of middlewares

[kevinGodell]

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Proposed changes

This change allows us to use our own authentication middleware in substitution for the built-in basic-auth middleware at the top level of RED.httpNode. The property httpNodeAuth in settings.js can receive a value that is a middleware function or array of middleware functions or fallback to using the built-in basic-auth. This change is backwards compatible. It was discussed on the forum @ https://discourse.nodered.org/t/httpnode-top-level-middleware-to-replace-basic-auth/85654/1

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the forum/slack team.
• I have run npm run test to verify the unit tests pass
• I have added suitable unit tests to cover the new/changed functionality