[HTTP] Help/remind developers to follow best practice of sending a `version`

[jloleysens]

We merged this PR which removes the dev-only requirement to send a version to a versioned HTTP APIs, we should explore ways to help developers not to neglect sending versions to public versioned HTTP APIs

From the linked PR's description:

...To better guide developers we can consider other options like: make version required in core's HTTP client [TS] interface (lots of updates...), doing something in tests, adding docs, something else or any combo of these.

...or consider some other approach.

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)