Alter availability formatting in OpenAPI format

[lcawl]

Relates to #2714, elastic/kibana#181995

The specification currently has @availability which encompasses the lifecycle of the API. For example in IndicesGetDataLifecycleRequest.ts

/**
* Get data stream lifecycles.
* Retrieves the data stream lifecycle configuration of one or more data streams.
* @rest_spec_name indices.get_data_lifecycle
* @availability stack since=8.11.0 stability=stable
* @availability serverless stability=stable visibility=public
*/

Currently we use it to output information like this in the openAPI docs:

"x-state": "Technical preview"
...
"x-state": "Added in 5.0.0"

We are trying to move toward having both serverless and stateful details within a single document, however, in which case something like this might be the simplest solution:

"x-state": "Serverless: Technical preview; Stack: Added in 5.0.0"

Once that information is output by the openapi generator, we could revisit the need to have separate serverless and stateful output files.