Don't modify user source code

[anuraaga]

Is your feature request related to a problem? Please describe.

Currently, when instrumenting, main.go gets modified with many blank imports. I think this is confusing to users and doesn't feel like "no-code". It is unavoidable to add code to support go mod tidy but it is best to not modify actual user code.

import _ "github.com/myproject/mymodule/example-alibaba/otel_rules"

import _ "go.opentelemetry.io/otel/exporters/prometheus"
import _ "go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp"
import _ "go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc"
import _ "go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp"
import _ "go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"
import _ "go.opentelemetry.io/otel/exporters/otlp/otlptrace"
import _ "go.opentelemetry.io/otel"

Describe the solution you'd like

Output blank imports to a separate file. For example, orchestrion outputs orchestrion.tool.go with build tag +tool. I think the build tag is overkill, but having a separate file is much nicer than having user code modified.

Describe alternatives you've considered

No response

Additional context

No response

[y1yang0]

Ideally, we will restore all modified files(code, go.mod, etc) after instrumentation, but it appears to be broken after latest commit, will fix #301