housekeep(fastapi): rework aurweb.db session API

Changes:
-------
- Add aurweb.db.get_session()
    - Returns aurweb.db's global `session` instance
    - Provides us a way to change the implementation of the session
      instance without interrupting user code.
- Use aurweb.db.get_session() in session API methods
- Add docstrings to session API methods
- Refactor aurweb.db.delete
    - Normalize aurweb.db.delete to an alias of session.delete
- Refresh instances in places we depend on their non-PK columns
  being up to date.

Signed-off-by: Kevin Morris <kevr@0cost.org>

aurweb/util.py

@@ -155,6 +155,7 @@ def get_ssh_fingerprints():
 def apply_all(iterable: Iterable, fn: Callable):
     for item in iterable:
         fn(item)
+    return iterable
 
 
 def sanitize_params(offset: str, per_page: str) -> Tuple[int, int]: