Don't duplicate version in __init__.py and pyproject.toml

Support of Python <= 3.7 is a bit more complicated.
To simplify when the support will be dropped.

django_auth_adfs/__init__.py

@@ -1,7 +1,10 @@
-"""
-Don't put imports or code here
-This file is imported by setup.py
-Adding imports here will break setup.py
-"""
+import sys
 
-__version__ = '1.11.0'
+if sys.version_info[:2] >= (3, 8):
+    from importlib import metadata
+else:
+    import importlib_metadata as metadata
+
+__version__ = metadata.version(__package__)
+
+del metadata  # optional, avoids polluting the results of dir(__package__)

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = 'django-auth-adfs'
-version = "1.11.0"  # Remember to also change __init__.py version
+version = "1.11.0"
 description = 'A Django authentication backend for Microsoft ADFS and AzureAD'
 authors = ['Joris Beckers <joris.beckers@gmail.com>']
 maintainers = ['Jonas Krüger Svensson <jonas-ks@hotmail.com>', 'Sondre Lillebø Gundersen <sondrelg@live.no>']
@@ -43,6 +43,7 @@ requests = '^1 || ^2'
 urllib3 = '^1.26.0'
 cryptography = '>=1.7,<39.0'
 PyJWT = "^2.4.0"
+importlib-metadata = {version = ">=1.7.0", python = "<3.8"}
 
 [tool.poetry.dev-dependencies]
 responses = '*'