MAINT: Add openstacksdk to setup.py

OpenstackSDK should be added to the install_requires. This is a list of
packages required for a minimal installation of the package. We can
leave out other packages in the requirements.txt as they are only used
to configure the environment.

setup.py

@@ -14,6 +14,9 @@
     long_description=LONG_DESCRIPTION,
     packages=find_packages(),
     python_requires=">=3.8",
-    install_requires=[],
+    install_requires=[
+        "openstacksdk",
+        "tabulate"
+        ],
     keywords=["python, openstack"],
 )