[Alerting V2] Review GA Alerting v2 OAS API docs

### Description

We are introducing the Alerting V2 feature set as GA in 9.6.0. A PR was merged to introduce the OAS generated docs for Alerting V2 with an experimental flag.

Ahead of GA, we want a more thorough review of the docs for clarity and consistency.

@nastasha-solomon mentioned these reviews typically consist of:

* Building the API docs locally to make sure there's no formatting or structural issues.
* Reviewing descriptions for newly added or updated endpoints, params, and descriptions against [this checklist](https://www.elastic.co/docs/contribute-docs/api-docs/checklist#content-quality-and-completeness) and [Elastic's writing style guide](https://www.elastic.co/docs/contribute-docs/style-guide) to ensure the content makes sense and is consistent with the writing standards.
* Making sure cross-repo or external links within the API doc changes work and doing some basic [QA checks](https://www.elastic.co/docs/contribute-docs/api-docs/checklist#quality-assurance), where possible.

### Resources

The OAS PR tagging the feature as experimental https://github.com/elastic/kibana/pull/279519

### Which deployment methods does this change impact?

Elastic On-Prem and Cloud (all)

### Feature differences

_No response_

### What Elastic Stack release is this request related to?

9.6

### Serverless release

_No response_

### Collaboration model

Other (please describe below)

### Point of contact.

**Main contact:** @dominiqueclarke @jasonrhodes

**Stakeholders:** RNA Project team

For collaboration, we've already technically created the first draft by publishing the existing OAS docs. We hope that the docs team can review those existing docs and suggest improvements.