fix: refuse to start with default secret on non debug envs

[dpgaspar]

SUMMARY

Impose harsher measures when a default SECRET_KEY is identified.
On non development environments on Flask debug mode Superset will refuse to start

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #23186 (96ff56e) into master (89576f8) will decrease coverage by 0.01%.
The diff coverage is 72.72%.

❗ Current head 96ff56e differs from pull request most recent head 9edf0c4. Consider uploading reports for the commit 9edf0c4 to get more accurate results

@@            Coverage Diff             @@
##           master   #23186      +/-   ##
==========================================
- Coverage   67.51%   67.51%   -0.01%     
==========================================
  Files        1899     1899              
  Lines       72990    72999       +9     
  Branches     7899     7899              
==========================================
+ Hits        49276    49282       +6     
- Misses      21689    21692       +3     
  Partials     2025     2025              

Flag	Coverage Δ
hive	52.86% <72.72%> (+<0.01%)	⬆️
mysql	78.48% <72.72%> (-0.01%)	⬇️
postgres	78.54% <72.72%> (-0.01%)	⬇️
presto	52.77% <72.72%> (+<0.01%)	⬆️
python	82.33% <72.72%> (-0.01%)	⬇️
sqlite	77.02% <72.72%> (-0.01%)	⬇️
unit	52.61% <72.72%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
superset/initialization/__init__.py	91.38% <70.00%> (-0.71%)	⬇️
superset/config.py	91.78% <100.00%> (ø)

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[villebro]

LGTM