ZDT - Version all Connector external HTTP APIs

[kobelb]

Feature Description

All external and publicly available HTTP APIs will need to abide by the Elastic HTTP API versioning guidance. As a result, they will need to abide by calendar versioning, and any breaking changes to said HTTP APIs will result in a new calendar version being released.

Business Value

Facilitates zero downtime rolling upgrades and rollbacks, allowing us to roll-out new features to our users more quickly while they continue to use the system without disruption.

Definition of Done

• All external and publicly available HTTP APIs are versioned
• Documentation is updated to reflect the version of the HTTP APIs
• HTTP API integration tests updated
• Unit tests

[kobelb]

/cc @elastic/response-ops-execution