add passreset routes

Introduced `get|post` `/passreset` routes. These routes mimic the
behavior of the existing PHP implementation, with the exception of
HTTP status code returns.

Routes added:
    GET /passreset
    POST /passreset

Routers added:
    aurweb.routers.accounts

* On an unknown user or mismatched resetkey (where resetkey must ==
  user.resetkey), return HTTP status NOT_FOUND (404).
* On another error in the request, return HTTP status BAD_REQUEST (400).

Both `get|post` routes requires that the current user is **not**
authenticated, hence `@auth_required(False, redirect="/")`.

+ Added auth_required decorator to aurweb.auth.
+ Added some more utility to aurweb.models.user.User.
+ Added `partials/error.html` template.
+ Added `passreset.html` template.
+ Added aurweb.db.ConnectionExecutor functor for paramstyle logic.
  Decoupling the executor logic from the database connection logic
  is needed for us to easily use the same logic with a fastapi
  database session, when we need to use aurweb.scripts modules.

At this point, notification configuration is now required to complete
tests involved with notifications properly, like passreset.
`conf/config.dev` has been modified to include [notifications] sendmail,
sender and reply-to overrides. Dockerfile and .gitlab-ci.yml have been
updated to setup /etc/hosts and start postfix before running tests.

* setup.cfg: ignore E741, C901 in aurweb.routers.accounts

These two warnings (shown in the commit) are not dangerous and a bi-product
of maintaining compatibility with our current code flow.

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

test/README.md

@@ -27,6 +27,7 @@ For all the test to run, the following Arch packages should be installed:
 - python-pytest
 - python-pytest-cov
 - python-pytest-asyncio
+- postfix
 
 Running tests
 -------------
@@ -37,6 +38,10 @@ First, setup the test configuration:
 
     $ sed -r 's;YOUR_AUR_ROOT;$(pwd);g' conf/config.dev > conf/config
 
+You'll need to make sure that emails can be sent out by aurweb.scripts.notify.
+If you don't have anything setup, just install postfix and start it before
+running tests.
+
 With those installed, one can run Python tests manually with any AUR config
 specified by `AUR_CONFIG`: