Fall back to generic WebApplicationStack

if we're building a web app, but aren't using gunicorn. I don't think
this has a big impact currently, since you can only set base pools via
lib/galaxy/main.py. I think you could set up alternative logging based
on the web stack class though, and this seems cleaner.

lib/galaxy/main_config.py

@@ -75,6 +75,7 @@ class WebappConfigResolver:
         self.is_ini_file = config_is_ini(self.config_file)
         self.config_section = self._resolve_section_name()
         self._update_kwds()
+        os.environ["IS_WEBAPP"] = "1"
 
     def resolve_config(self) -> WebappConfig:
         global_conf = {}

lib/galaxy/web_stack/__init__.py

@@ -291,6 +291,8 @@ def application_stack_class() -> Type[ApplicationStack]:
     """
     if "gunicorn" in os.environ.get("SERVER_SOFTWARE", ""):
         return GunicornApplicationStack
+    elif os.environ.get("IS_WEBAPP") == "1":
+        return WebApplicationStack
     return WeblessApplicationStack