Omitted Serverless API content during migration

[florent-leborgne]

As reported by @juliocamarero, useful serverless API examples were lost:

"The API Principles and Authentication have been copied there. However, 2 sections are not there... and for the examples it probably makes sense since the API reference is probably not the best place to have this "user guide" with some quick examples... but I tend to see some value in the old page."

Missing content is currently still in asciidoc here: https://github.com/elastic/docs-content/blob/main/serverless/pages/manage-your-project-rest-api.asciidoc

What to do

• Find/discuss the best place for this content (Somewhere in the new docs, or in the API docs?)
• Add it

[lcawl]

My two cents is that the content in that asciidoc source file from "To try the examples in this section..." to "You can store the project ID as an environment variable for the next requests..." makes sense to add to the OpenAPI document. Either in the document's description field or in a supplementary page in the "Topics" section (using x-topics per https://docs.bump.sh/help/documentation-experience/topics/).

My expectation would be the subsequent examples in that page would be added to the appropriate endpoints.