fix(superset.cli): superset cli group doesn't support superset extension app

[ofekisr]

SUMMARY

When you run the Superset app, the app is loaded via Flask. Flask determines how to load the app by the FLASK_APP env variable.
In case you would like to develop an app that extends Superset, you can extend the app creation by supplying alternative FLASK_APP value instead of FLASK_APP="superset.app:create_app()"

but the Superset Cli group ignores that value by passing a redundant argument to FlaskGroup.

When the create_app argument is missed, it creates the application the same way the app is created on running Flask app

so when I set alternative value for Flask_app I can run superset init on the extended superset app

[codecov]

Codecov Report

Merging #17539 (a060b19) into master (7353a2b) will decrease coverage by 0.02%.
The diff coverage is n/a.

❗ Current head a060b19 differs from pull request most recent head 8bc5e2c. Consider uploading reports for the commit 8bc5e2c to get more accurate results

@@            Coverage Diff             @@
##           master   #17539      +/-   ##
==========================================
- Coverage   76.81%   76.79%   -0.03%     
==========================================
  Files        1049     1049              
  Lines       56653    56652       -1     
  Branches     7847     7847              
==========================================
- Hits        43517    43504      -13     
- Misses      12883    12895      +12     
  Partials      253      253              

Flag	Coverage Δ
mysql	82.00% <ø> (-0.01%)	⬇️
postgres	82.01% <ø> (-0.01%)	⬇️
python	82.06% <ø> (-0.05%)	⬇️
sqlite	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
superset/cli.py	54.82% <ø> (-0.11%)	⬇️
superset/db_engine_specs/sqlite.py	91.89% <0.00%> (-5.41%)	⬇️
superset/connectors/sqla/utils.py	88.23% <0.00%> (-3.93%)	⬇️
superset/utils/celery.py	86.20% <0.00%> (-3.45%)	⬇️
superset/result_set.py	96.77% <0.00%> (-1.62%)	⬇️
superset/utils/cache.py	73.58% <0.00%> (-0.95%)	⬇️
superset/db_engine_specs/base.py	87.62% <0.00%> (-0.59%)	⬇️
superset/models/slice.py	84.72% <0.00%> (-0.50%)	⬇️

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[craig-rueda]

LGTM

[craig-rueda]

Can you update the UPDATING.md as this might affect some users.

[ofekisr]

@craig-rueda

Can you update the UPDATING.md as this might affect some users.

done

[john-bodley]

@ofekisr this change—though relevant for inclusion in UPDATING.md—should be housed under the "Breaking Changes" section as opposed to "Potential Downtime".

[ofekisr]

How does it breaking change?