Added asgiref depedency to opentelemetry-instrumentation-asgi

opentelemetry-instrumentaiton-asgi does not contain an instrumentor for
asgiref. Instead, it implements an ASGI middleware that other
instrumentors import and use. As such, other instrumentors can take a
dependency on this package without asgiref being installed locally. This
commit adds `asgiref` as a dependency to the
opentelemetry-instrumentation-asgi package so the middleware can
function properly when used by another instrumentation.

CHANGELOG.md

@@ -6,6 +6,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased](https://github.com/open-telemetry/opentelemetry-python/compare/v1.6.2-0.25b2...HEAD)
+### Fixed
+
+- `opentelemetry-instrumentation-asgi` now explicitly depends on asgiref as it uses the package instead of instrumenting it.
+  ([#765](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/765))
 
 ## [1.6.2-0.25b2](https://github.com/open-telemetry/opentelemetry-python/releases/tag/v1.6.2-0.25b2) - 2021-10-19
 

instrumentation/opentelemetry-instrumentation-asgi/setup.cfg

@@ -43,6 +43,7 @@ install_requires =
     opentelemetry-semantic-conventions == 0.25b2
     opentelemetry-instrumentation == 0.25b2
     opentelemetry-util-http == 0.25b2
+    asgiref ~= 3.0
 
 [options.extras_require]
 test =