explain auto and manual

Actually it's not what I initially thought here, in Java:

for elastic agent auto means using the -javaagent setup option, which we call "manual" in our documentation: https://www.elastic.co/guide/en/apm/agent/java/current/setup-javaagent.html
for elastic agent manual means there is a minor code modification to use the runtime attach setup: https://www.elastic.co/guide/en/apm/agent/java/current/setup-attach-api.html
for otel, the manual option means explicit code changes in the app to capture traces by using only the otel API/SDK without an agent.
for otel , the auto means using the otel instrumentation agent with the -javaagent setup option, and no code modification is needed in the application (because the otel agent has automatic instrumentation for the used framework/libraries).

I think here we should probably rename and simplify things if we want to be consistent:

use the manual for the explicit tracing, which requires few changes to the application code
maybe leave the different setup options (like runtime attach and -javaagent) outside of the scope of what is shown here, as they don't provide much value and are quite well documented, also we have 3 of them in java doc.
With Elastic agent there is no "manual tracing", as it's not possible to use the tracing API without the agent. If we go this route, then only the otel agent would have a "manual".

elastic / observability-examples