applicactions: fix applications:

This patch fix application configuration parsing. Peertube and Weblate can be started
again.

libervia/backend/plugins/plugin_misc_app_manager/__init__.py

@@ -150,7 +150,7 @@ class AppManager:
                     )
                     data["_instance_dir_obj"].cleanup()
 
-    def _libervia_conf_constr(self, loader, node) -> str:
+    def _libervia_conf_constr(self, loader, node) -> str|None:
         """Get a value from Libervia configuration
 
         A list is expected with either "name" of a config parameter, a one or more of
@@ -178,7 +178,21 @@ class AppManager:
                 "is expected"
             )
 
-        value = getattr(getattr(G.config, section), name) or default
+        try:
+            if section.startswith("application."):
+                key  = section[12:].strip()
+                if not key:
+                    raise ValueError("Invalid configuration section: {section!r}}")
+                value = G.config.application.get(key, {}).get(name, default)
+            else:
+                value = getattr(getattr(G.config, section), name) or default
+        except (AttributeError, KeyError):
+            from pudb import set_trace; set_trace()
+            raise ValueError(
+                f"Invalid configuration request: {section=}, {name=}, {default=}, "
+                f"{filter=}"
+            )
+
         # FIXME: "public_url" is used only here and doesn't take multi-sites into account
         if name == "public_url" and (not value or value.startswith("http")):
             if not value:
@@ -201,9 +215,11 @@ class AppManager:
         if filter_ is None:
             pass
         elif filter_ == "first":
+            if not value:
+                raise ValueError("Invalid value: {value!r}")
             value = value[0]
         elif filter_ == "not":
-            value = C.bool(value)
+            assert isinstance(value, bool)
             value = C.bool_const(not value).lower()
         else:
             raise ValueError(f"unmanaged filter: {filter_}")