Add missing NEEDED features up to OSB v1.27

[frigaut-orange]

This repo is compatible with the OSB spec v1.24. We want compatibility up to v1.27.

Here are the missing features that we absolutely need and will use for now. Further development will be needed afterwards for other features.

• 2.15
  • Header request identity
  • Endpoints in bind request response body
• 2.16
  • Missing metadata in service instance provisioning/updating response body
  • Missing metadata in service binding creation response body
• 2.17
  • Binding rotation mechanisms
  • Missing metadata in service instance and binding fetch response bodies

Unit tests should be added and updated accordingly.