Otel docs updates

[estolfo]

@szabosteve kindly did a review of the docs I wrote to accompany my native OpenTelemetry implementation in the ES Ruby client. I used many of the docs from this repo to write that one, so I'm applying some of the changes here as well.

Here is the commit from the ruby repo: https://github.com/elastic/elasticsearch-ruby/pull/2179/commits/bb7b6123bc154355d5631b4bfb3c6c62955c6a0c

cc @AlexanderWert