♻️ Move the push configuration into the backwards compat as well

Consistent with
#961 (comment)
and
- 3dea305 (example for the api)
- 7f1be92 (original example for the database)

Testing done:

```
$ ./e-mission-py.bash emission/tests/netTests/TestPush.py
----------------------------------------------------------------------
Ran 5 tests in 0.276s

OK
```

emission/net/ext_service/push/notify_interface.py

@@ -11,22 +11,26 @@
 import logging
 import importlib
 
-import emission.net.ext_service.push.config as pc
+import emission.core.backwards_compat_config as ecbc
 
 # Note that the URL is hardcoded because the API endpoints are not standardized.
 # If we change a push provider, we will need to modify to match their endpoints.
 # Hardcoding will remind us of this :)
 # We can revisit this if push providers eventually decide to standardize...
 
+push_config = ecbc.get_config('conf/net/ext_service/push.json',
+    {"PUSH_PROVIDER": "provider", "PUSH_SERVER_AUTH_TOKEN": "server_auth_token",
+     "PUSH_APP_PACKAGE_NAME": "app_package_name", "PUSH_IOS_TOKEN_FORMAT": "ios_token_format"})
+
 try:
-    push_config = pc.get_config()
+    logging.info(f"Push configured for app {push_config.get('PUSH_SERVER_AUTH_TOKEN')} using platform {os.getenv('PUSH_PROVIDER')} with token {os.getenv('PUSH_SERVER_AUTH_TOKEN')[:10]}... of length {len(os.getenv('PUSH_SERVER_AUTH_TOKEN'))}")
 except:
     logging.warning("push service not configured, push notifications not supported")
 
 class NotifyInterfaceFactory(object):
     @staticmethod
     def getDefaultNotifyInterface():
-        return NotifyInterfaceFactory.getNotifyInterface(push_config["provider"])
+        return NotifyInterfaceFactory.getNotifyInterface(push_config["PUSH_PROVIDER"])
 
     @staticmethod
     def getNotifyInterface(pushProvider):

emission/net/ext_service/push/notify_interface_impl/firebase.py

@@ -21,13 +21,13 @@ def get_interface(push_config):
 
 class FirebasePush(pni.NotifyInterface):
     def __init__(self, push_config):
-        self.server_auth_token = push_config["server_auth_token"]
-        if "app_package_name" in push_config:
-            self.app_package_name = push_config["app_package_name"]
+        self.server_auth_token = push_config["PUSH_SERVER_AUTH_TOKEN"]
+        if "PUSH_APP_PACKAGE_NAME" in push_config:
+            self.app_package_name = push_config["PUSH_APP_PACKAGE_NAME"]
         else:
             logging.warning("No package name specified, defaulting to embase")
             self.app_package_name = "edu.berkeley.eecs.embase"
-        self.is_fcm_format = push_config["ios_token_format"] == "fcm"
+        self.is_fcm_format = push_config["PUSH_IOS_TOKEN_FORMAT"] == "fcm"
 
     def get_and_invalidate_entries(self):
         # Need to figure out how to do this on firebase

emission/tests/netTests/TestPush.py

@@ -121,7 +121,7 @@ def testFcmMapping(self):
         logging.debug("test token map = %s" % self.test_token_map)
 
         try:
-            fcm_instance = pnif.get_interface({"server_auth_token": "firebase_api_key", "ios_token_format": "apns"})
+            fcm_instance = pnif.get_interface({"PUSH_SERVER_AUTH_TOKEN": "firebase_api_key", "PUSH_IOS_TOKEN_FORMAT": "apns"})
             (mapped_token_map, unmapped_token_list) = fcm_instance.map_existing_fcm_tokens(self.test_token_map)
             # At this point, there is nothing in the database, so no iOS tokens will be mapped
             self.assertEqual(len(mapped_token_map["ios"]), 0)
@@ -176,7 +176,7 @@ def testFcmNoMapping(self):
             "android": self.test_token_list_android}
         logging.debug("test token map = %s" % self.test_token_map)
 
-        fcm_instance = pnif.get_interface({"server_auth_token": "firebase_api_key", "ios_token_format": "fcm"})
+        fcm_instance = pnif.get_interface({"PUSH_SERVER_AUTH_TOKEN": "firebase_api_key", "PUSH_IOS_TOKEN_FORMAT": "fcm"})
         (mapped_token_map, unmapped_token_list) = fcm_instance.map_existing_fcm_tokens(self.test_token_map)
         # These are assumed to be FCM tokens directly, so no mapping required
         self.assertEqual(len(mapped_token_map["ios"]), 10)