docs: Add missing dependencies and fix django (#657)

- Add missing sqlalchemy and django dependencies
- Configure django in docs/conf.py to avoid non configured exeception

Author: mauriciovasquezbernal

Diff for: docs-requirements.txt

@@ -5,6 +5,7 @@ sphinx-autodoc-typehints~=1.10.2
 # Required by ext packages
 aiohttp ~= 3.0
 Deprecated>=1.2.6
+django>=2.2
 PyMySQL~=0.9.3
 flask~=1.0
 mysql-connector-python~=8.0
@@ -13,5 +14,6 @@ prometheus_client>=0.5.0,<1.0.0
 psycopg2-binary>=2.7.3.1
 pymongo~=3.1
 redis>=2.6
+sqlalchemy>=1.0
 thrift>=0.10.0
 wrapt >=1.0.0,<2.0.0

Diff for: docs/conf.py

@@ -15,6 +15,15 @@
 from os import listdir
 from os.path import isdir, join
 
+# configure django to avoid the following exception:
+# django.core.exceptions.ImproperlyConfigured: Requested settings, but settings
+# are not configured. You must either define the environment variable
+# DJANGO_SETTINGS_MODULE or call settings.configure() before accessing settings.
+from django.conf import settings
+
+settings.configure()
+
+
 source_dirs = [
     os.path.abspath("../opentelemetry-api/src/"),
     os.path.abspath("../opentelemetry-sdk/src/"),