[DOCS] Add minimal specifications for all Elasticsearch API docs

[lcawl]

In order to retire the old API documentation, we need specifications for each API that appears in the old docs unless the API is internal or being removed. The following APIs do not yet appear in the OpenAPI document:

• Post event to an analytics collection Add specification for post event to an analytics collection #3363
• Update connector features Add specification for update connector features #3364
• Check in connector sync job Add specification for check in connector sync job #3365
• Claim connector sync job Add specification for claim connector sync job #3366
• Set connector sync job error Add specification for set connector sync job error #3367
• Set connector sync job stats Add specification for set connector sync job stats #3368
• Find field structure Add find field structure and find messages structure APIs #3346
• Find messages structure Add find field structure and find messages structure APIs #3346
• Get data stream lifecycle stats
• ES|QL async query
• ES|QL async query get
• ES|QL async query delete