feat: import external management columns

[betodealmeida]

SUMMARY

Allow imports to pass is_managed_externally and external_url to indicate that these assets are being managed outside of Superset. Currently this is just stored as metadata, but in the future the columns should be used to disable edits and point users to the source of truth where the resources can be managed.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N/A

TESTING INSTRUCTIONS

Added unit tests.

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 #19315 (b043c2d) into master (7ca10fb) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

❗ Current head b043c2d differs from pull request most recent head 53d6a7c. Consider uploading reports for the commit 53d6a7c to get more accurate results

@@            Coverage Diff             @@
##           master   #19315      +/-   ##
==========================================
- Coverage   66.65%   66.63%   -0.03%     
==========================================
  Files        1672     1672              
  Lines       64611    64622      +11     
  Branches     6505     6505              
==========================================
- Hits        43066    43060       -6     
- Misses      19862    19879      +17     
  Partials     1683     1683              

Flag	Coverage Δ
hive	52.66% <100.00%> (+0.01%)	⬆️
mysql	?
postgres	81.70% <100.00%> (-0.01%)	⬇️
presto	52.51% <100.00%> (+0.01%)	⬆️
python	82.07% <100.00%> (-0.05%)	⬇️
sqlite	81.48% <100.00%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
superset-frontend/src/views/components/Menu.tsx	60.00% <ø> (ø)
superset/charts/schemas.py	99.34% <100.00%> (+<0.01%)	⬆️
superset/connectors/base/models.py	88.65% <100.00%> (+0.03%)	⬆️
superset/dashboards/schemas.py	99.42% <100.00%> (+<0.01%)	⬆️
superset/databases/schemas.py	98.49% <100.00%> (+0.01%)	⬆️
superset/datasets/schemas.py	97.22% <100.00%> (+0.03%)	⬆️
superset/models/core.py	88.33% <100.00%> (-0.72%)	⬇️
superset/models/dashboard.py	75.57% <100.00%> (+0.09%)	⬆️
superset/models/slice.py	85.43% <100.00%> (+0.07%)	⬆️
superset/common/utils/dataframe_utils.py	85.71% <0.00%> (-7.15%)	⬇️
... and 7 more

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[pkdotson]

lgtm!