fix(alert/report): switch message content between chart and dashboard

[lilykuang]

SUMMARY

• when switching dashboard/chart in message content AlertReportModal, it clears dashboard or chat field

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

After:
https://www.loom.com/share/6c410a0354224656aa3200f620c69173

TEST PLAN

ADDITIONAL INFORMATION

• Has associated issue: [Alerts & Reports] Can't switch 'Message content' from a Chart to a Dashboard #13207
• Changes UI
• Requires DB Migration.
• Confirm DB Migration upgrade and downgrade tested.
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #13537 (63f1c60) into master (fc36de2) will decrease coverage by 0.01%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master   #13537      +/-   ##
==========================================
- Coverage   76.93%   76.92%   -0.02%     
==========================================
  Files         934      934              
  Lines       46310    46310              
  Branches     5647     5645       -2     
==========================================
- Hits        35629    35622       -7     
- Misses      10547    10554       +7     
  Partials      134      134              

Flag	Coverage Δ
cypress	57.46% <ø> (-0.01%)	⬇️
hive	80.13% <100.00%> (+0.01%)	⬆️
javascript	62.44% <0.00%> (ø)
mysql	?
postgres	?
presto	80.17% <100.00%> (?)
python	80.86% <100.00%> (-0.03%)	⬇️
sqlite	80.12% <100.00%> (ø)

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

Impacted Files	Coverage Δ
...frontend/src/views/CRUD/alert/AlertReportModal.tsx	56.00% <0.00%> (ø)
superset/reports/schemas.py	98.61% <100.00%> (ø)
superset/sql_validators/postgres.py	50.00% <0.00%> (-50.00%)	⬇️
superset/databases/commands/create.py	82.35% <0.00%> (-9.81%)	⬇️
superset/databases/commands/update.py	85.71% <0.00%> (-8.17%)	⬇️
superset/db_engine_specs/mysql.py	89.79% <0.00%> (-2.05%)	⬇️
superset/databases/api.py	90.32% <0.00%> (-1.62%)	⬇️
...set-frontend/src/dashboard/util/getDropPosition.js	90.90% <0.00%> (-1.52%)	⬇️
superset/models/core.py	88.01% <0.00%> (-0.55%)	⬇️
superset/common/query_context.py	81.52% <0.00%> (-0.55%)	⬇️
... and 4 more

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