[OAS] Add a description for each response

[lcawl]

Describe the feature:

Relates to #228077

When you run node ./scripts/validate_oas_docs.js or when it runs as a CI check, there are a lot of messages like this:

 /paths/~1api~1fleet~1settings/get/responses/200
   │      must have required property 'description'
   │
   │      /paths/~1api~1fleet~1settings/get/responses/400
   │      must have required property 'description'
   │
   │      /paths/~1api~1fleet~1settings/get/responses/404
   │      must have required property 'description'
   │
   │      /paths/~1api~1fleet~1settings/put/responses/200
   │      must have required property 'description'

I believe this occurs because a lot of the responses (particularly those in the parts of the OpenAPI document that are generated from the code) are missing descriptions. For an example of how it can be added in those cases, refer to https://github.com/elastic/kibana/blob/main/x-pack/platform/plugins/shared/actions/server/routes/connector/create/create.ts#L43

Describe a specific use case for the feature:

By addressing all the missing descriptions, we can start reduce the volume of validation errors and hopefully get the OpenAPI document to a state of validity that enables us to use it for things like Terraform resource generation.

[elasticmachine]

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

NOTE: When I first opened this issue I thought the functionality was absent, but further investigation indicates it's there so this is just a matter of adding the missing content instead.

[elasticmachine]

Pinging @elastic/experience-docs (Team:Docs)

[florent-leborgne]

@lcawl do you already have a plan in mind for this or should we look into distributing the work?

[lcawl]

In the latest release (OpenAPI 3.2), the response description is no longer mandatory per OAI/OpenAPI-Specification#4500. Therefore IMO rather than adding all these descriptions, we should mute that linting message.

[tobio]

In the latest release (OpenAPI 3.2), the response description is no longer mandatory per OAI/OpenAPI-Specification#4500. Therefore IMO rather than adding all these descriptions, we should mute that linting message.

We're publishing a spec with v3.0.3 though, so the spec remains invalid. This creates issues for consumers where tooling expects a valid spec file. Multiple code generators fail fast based on the schema check which makes the Kibana spec unusable as published without these descriptions.