fix: Ensure alerts & reports aren't schduled when flag is off

[jfrag1]

SUMMARY

Currently, if there are active alerts & reports, they will be triggered even if the ALERT_REPORTS flag is turned off. This is a rare case, but it would make sense to stop these from triggering if the feature is off.

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 #16639 (7ca9f67) into master (788c0c3) will decrease coverage by 0.20%.
The diff coverage is 100.00%.

❗ Current head 7ca9f67 differs from pull request most recent head ac85a02. Consider uploading reports for the commit ac85a02 to get more accurate results

@@            Coverage Diff             @@
##           master   #16639      +/-   ##
==========================================
- Coverage   76.76%   76.56%   -0.21%     
==========================================
  Files        1004     1004              
  Lines       53967    53985      +18     
  Branches     7335     7335              
==========================================
- Hits        41430    41333      -97     
- Misses      12298    12413     +115     
  Partials      239      239              

Flag	Coverage Δ
hive	?
mysql	81.59% <100.00%> (+0.05%)	⬆️
postgres	81.62% <100.00%> (+0.05%)	⬆️
presto	?
python	81.70% <100.00%> (-0.41%)	⬇️
sqlite	81.26% <100.00%> (+0.01%)	⬆️

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

Impacted Files	Coverage Δ
superset/reports/api.py	88.46% <ø> (+0.67%)	⬆️
superset/models/slice.py	86.41% <100.00%> (ø)
superset/reports/commands/create.py	88.52% <100.00%> (+1.25%)	⬆️
superset/reports/commands/exceptions.py	98.91% <100.00%> (+0.03%)	⬆️
superset/reports/dao.py	83.46% <100.00%> (+1.11%)	⬆️
superset/tasks/scheduler.py	68.88% <100.00%> (+1.44%)	⬆️
superset/db_engines/hive.py	0.00% <0.00%> (-82.15%)	⬇️
superset/db_engine_specs/hive.py	69.80% <0.00%> (-16.87%)	⬇️
superset/db_engine_specs/presto.py	83.47% <0.00%> (-6.49%)	⬇️
superset/views/database/mixins.py	81.03% <0.00%> (-1.73%)	⬇️
... and 5 more

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[jfrag1]

Anyone with merge powers feel free to hit the button :)