PR - [feature]: Add middlware to retrieve settings

[dave-ok]

PR Checklist

• Run npm run lint to find errors in code syntax/format
• Run npm run lint:fix to fix all auto-fixable errors in source code and auto-format with prettier
• Ensure you fix any linting errors displayed after running any of the above commands

What does this PR do

Fixes #538

A middleware to retrieve remote settings on each request, parse and validate settings, and attach settings to request object, for availability down the middleware chain in the request/response cycle

Description of Task to be completed

• Create settings parser
• Add validation option to parser
• Write tests for parser
• Create middleware to
  • validate API key,
  • decode projectID from API key signed with a shared secret,
  • retrieve settings for given projectID,
  • parse and validate returned settings
  • attach projectID and settings on request object
• Write tests for middleware

How should this be manually tested

Run npm run test src/utils/__test__/settingsParser.test.js to test settings parser/validator
Run npm run test src/middleware/__test__/settings.test.js to test middleware

Any background context you want to provide

The settings middleware currently pulls mocked settings from a function in src/utils/mocks/settings which will be replaced by the actual settings provider when implemented

[dave-ok]

Closed to reopen from fork