Create celery_app even if there is no broker_url for integ test

[javierdelapuente]

Applicable spec:

Overview

For the examples for workers and schedulers, create always the Celery app, even if there is no broker url. That way, the rockcrack.yaml file does not need to be run with bash (as Celery will always start), and sets a better example of use for the background tasks.

Suggested by @amandahla #44 (comment). Thanks!

Rationale

Juju Events Changes

Module Changes

Library Changes

Checklist

• The charm style guide was applied
• The contributing guide was applied
• The changes are compliant with ISD054 - Managing Charm Complexity
• The documentation is generated using src-docs
• The documentation for charmhub is updated
• The PR is tagged with appropriate label (urgent, trivial, complex)

[github-actions]

Test coverage for 1fdd8b6

Name                                            Stmts   Miss Branch BrPart  Cover   Missing
-------------------------------------------------------------------------------------------
paas_app_charmer/__init__.py                       32     17      0      0    47%   13-14, 19-20, 26-27, 33-37, 43-44, 50-51, 57-58
paas_app_charmer/_gunicorn/__init__.py              0      0      0      0   100%
paas_app_charmer/_gunicorn/charm.py                15      0      0      0   100%
paas_app_charmer/_gunicorn/webserver.py            83      4     16      1    95%   175, 187-193
paas_app_charmer/_gunicorn/workload_config.py       8      0      0      0   100%
paas_app_charmer/_gunicorn/wsgi_app.py             16      0      0      0   100%
paas_app_charmer/app.py                           152      0     64      3    99%   110->exit, 160->166, 334->336
paas_app_charmer/charm.py                         232     25     52      3    89%   33-34, 41-42, 205-206, 208-209, 242-246, 303-305, 359-360, 365, 370, 375, 385, 390, 395, 400, 405, 430
paas_app_charmer/charm_state.py                   108      2     20      2    97%   188, 278
paas_app_charmer/charm_utils.py                    23      0      0      0   100%
paas_app_charmer/database_migration.py             35      0      2      0   100%
paas_app_charmer/databases.py                      25      2     11      1    92%   89-90
paas_app_charmer/django/__init__.py                 2      0      0      0   100%
paas_app_charmer/django/charm.py                   42      4     10      2    88%   44, 104, 119-120
paas_app_charmer/exceptions.py                      5      0      0      0   100%
paas_app_charmer/fastapi/__init__.py                2      0      0      0   100%
paas_app_charmer/fastapi/charm.py                  29      0      0      0   100%
paas_app_charmer/flask/__init__.py                  2      0      0      0   100%
paas_app_charmer/flask/charm.py                    24      0      0      0   100%
paas_app_charmer/go/__init__.py                     2      0      0      0   100%
paas_app_charmer/go/charm.py                       26      0      0      0   100%
paas_app_charmer/observability.py                  24      3      8      1    81%   42->46, 73-77
paas_app_charmer/rabbitmq.py                       78      2     22      5    93%   117->exit, 122->exit, 157->exit, 159-160, 181->175
paas_app_charmer/secret_storage.py                 50      2     16      4    91%   55->54, 56->58, 86, 105
paas_app_charmer/utils.py                          21      4     14      2    71%   30, 32, 52-53
-------------------------------------------------------------------------------------------
TOTAL                                            1036     65    235     24    92%

Static code analysis report

Run started:2024-09-27 08:15:00.452900

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 2248
  Total lines skipped (#nosec): 1
  Total potential issues skipped due to specifically being disabled (e.g., #nosec BXXX): 0

Run metrics:
  Total issues (by severity):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
  Total issues (by confidence):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
Files skipped (0):