Console support for REST API compatiblity

[jakelandis]

Describe the feature:

Staring in 8.0.0, Elasticsearch will support a custom header to request supporting compatible requests and responses with the prior major version (i.e. 7.x). Ideally, the dev console would be able to support this custom header. To enable compatibility per request (for JSON), the header is value is application/vnd.elasticsearch+json;compatible-with=7. This value is used instead of application/json for the Accept and the Content-Type header.

Describe a specific use case for the feature:

This likely isn't a common feature in 8.0.0 since it is opt-in (and brand new). However, this will help consumers that do opt to use REST API compatibility better align the shape of the request and response with that of their client that has this enabled. Most clients expose an all or nothing approach to sending the special header, so I would recommend that for dev console as well. For example, an option in the "Settings" to use REST API compatibility that changes which header is sent. It is safe to send this custom header to any endpoint that accepts normal JSON requests.

Unfortunately there is not a good way to differentiate which APIs will change based on enabling this header, nor is there a good way to identify the exact shape of the request/response for the prior major version.

[elasticmachine]

Pinging @elastic/kibana-stack-management (Team:Stack Management)

[cjcenizal]

Per Jake, the use cases for this feature are largely for troubleshooting, not primary use cases. As such, it's a non-critical feature for 8.0. Ideally we'd implement it sometime early in 8.x.

[elasticmachine]

Pinging @elastic/kibana-management (Team:Kibana Management)