Add setuptools intsrumentation install requirement

The `setuptools` package is not part of the stdlib, but often available
in the system environment (it is a buildtime requirement).

`pkg_resources` (a package provided by `setuptools`) is used as
a runtime requirement in `opentelemetry-instrumentation`. Explicitly
listing `setuptools` as a requirement protects instrumentation from
breaking with import errors in cases where `setuptools` is not available
system-wide.

For example:

* A multi-stage Docker build where the final image does not contain
buildtime requirements.
* A build system that packages the runtime dependencies into a single
binary.

This commit pins `setuptools >= 16.0` because that is the first release
that included all 5 imports instrumentation currently relies on.

CHANGELOG.md

@@ -8,6 +8,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased](https://github.com/open-telemetry/opentelemetry-python/compare/v1.6.2-0.25b2...HEAD)
 - `opentelemetry-instrumentation-aws-lambda` Add instrumentation for AWS Lambda Service - pkg metadata files (Part 1/2)
   ([#739](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/739))
+- `opentelemetry-instrumentation` Add `setuptools` to `install_requires`
+  ([#781](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/781))
 
 ### Fixed
 

opentelemetry-instrumentation/setup.cfg

@@ -42,6 +42,7 @@ zip_safe = False
 include_package_data = True
 install_requires =
     opentelemetry-api ~= 1.4
+    setuptools >= 16.0
     wrapt >= 1.0.0, < 2.0.0
 
 [options.packages.find]