Restructure Jaeger exporter SDK env var section

[pellared]

Fixes #2357

Changes

Restructure Jaeger exporter section so that it should be a more readable (from both markdown and "rendered version" perspective).

Preview here

Alternatives

I was trying to adopt the approach from #2345, however:

1. It was hard to fit into the current document structure. It looked awkward when compared to other sections in the same document.
2. I found it less readable.
3. This section is less frequently changing than the OTLP exporter equivalent.

[carlosalberto]

Ping @yurishkuro ;)