Fix and update integration tests (#163)

The API client is a singleton, and many integration tests had issues
running because the client got disconnected. Also the event loop was
scoped for the session rather than per function (default set in
pyproject.toml).
So the client was updated so that it reconnects for each test to ensure
its internal state is not corrupted and the event loop
is now function scoped.
Also the tests were updated to use the new endpoints and remove the ones
that no longer exist.

Author: daniel-zullo-frequenz

.github/workflows/integration_test.yml

@@ -15,7 +15,7 @@ jobs:
       fail-fast: false
       matrix:
         os:
-          - ubuntu-20.04
+          - ubuntu-24.04
         python:
           - "3.11"
     runs-on: ${{ matrix.os }}
@@ -51,5 +51,3 @@ jobs:
         run: |
           pytest -vv integration_tests/
         timeout-minutes: 10
-
-