Clarify "automatic instrumentation" term

[pellared]

Fixes #2336

Relates to open-telemetry/opentelemetry-dotnet-instrumentation#958

Relates to open-telemetry/opentelemetry.io#1565

Changes

Clarify "automatic instrumentation" term by removing some fragments that can bring confusion.

1. Remove "to use the OpenTelemetry APIs" which some may think that library instrumentation is a type of automatic instrumentation
2. Remove "access application code". Personally, I think that e.g. "assembly weaving" (instrumentation done as part of "compilation") is also a kind of automatic instrumentation. For some languages, like .NET, source code is not required, but I imagine some interpreted languages require accessing the code anyway 🤷 I just think that we can remove this part.
3. Change "application code" to "application's source code". To make it more obvious that it is "source code" and e.g. not "bytecode".

[pellared]

@tedsuo @cartermp @chalin @cijothomas PTAL

[pellared]

PTAL @open-telemetry/instr-wg @open-telemetry/java-instrumentation-approvers @open-telemetry/dotnet-instrumentation-approvers

[yurishkuro]

I don't think we should be removing reference to OTEL APIs, on the contrary, we should be emphasizing it, but clarifying. Specifically, an auto-instrumentation that attaches to the code at runtime and somehow exports OTEL-compatible data, would NOT be a compliant auto-instrumentation in my view, because:

• it breaks the API/SDK separation envisioned in the OTEL
• it likely does not allow adding manual instrumentation on top of automatic, because the manual instrumentation has to go through OTEL API.

[pellared]

@yurishkuro How about adding:

The automatic instrumentation MUST:

- use (directly or indirectly) the OpenTelemetry APIs,
- allow adding manual instrumentation.

? Any better proposal?

However, I am not sure if this kind of detail should be contained in the glossary. Maybe there should be a dedicated document/spec describing automatic instrumentation (it rather should not be part of this PR).

[pellared]

I will be AFK for a month. If there will be any blocking feedback then I am OK if someone addresses it on my branch. I allowed edits and access to secrets by maintainers. Of course, this PR can also be closed and someone can open a new one.

But maybe it is already good enough to be merged 🤞