[DOCS] Fix Create Logstash pipeline API page

[KOTungseth]

In the API docs, we say that id is required, but this is no longer accurate and is breaking user apps.

@joshdover can you confirm this? And what version does this apply to?

[elasticmachine]

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

[joshdover]

It looks like we relaxed this requirement in #76616 to fix a validation bug. So the id is required in the URL path, but not in the body any longer. I think we can just revert #71726 from 7.8+