build: update webpack for npm linking plugins

[ktmud]

SUMMARY

Update webpack config so that developers can npm link .../plugin-path without also having to npm link ../path/to/superset-ui/packages/superset-ui-core/. Currently you have to do the additional linking because npm link will install its own version of @superset-ui/core under the plugin's node_modules, which will take precedent for the plugin's JS modules during module resolution.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N/A

TEST PLAN

1. clone the superset-ui repo
2. npm link a plugin npm link ~/projects/superset-ui/plugins/legacy-preset-chart-nvd3/ in superset-frontend
3. Your plugin should show up in viz type selection

ADDITIONAL INFORMATION

• Has associated issue:
• Changes UI
• Requires DB Migration.
• Confirm DB Migration upgrade and downgrade tested.
• Introduces new feature or API
• Removes existing feature or API

cc @rusackas @villebro

[ktmud]

Not sure whether this will help but it definitely looks more reasonable than current setup.

[codecov-io]

Codecov Report

Merging #11253 into master will decrease coverage by 5.50%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #11253      +/-   ##
==========================================
- Coverage   65.59%   60.08%   -5.51%     
==========================================
  Files         832      394     -438     
  Lines       39448    24757   -14691     
  Branches     3598        0    -3598     
==========================================
- Hits        25874    14876   -10998     
+ Misses      13465     9881    -3584     
+ Partials      109        0     -109     

Flag	Coverage Δ
#cypress	?
#javascript	?
#python	60.08% <ø> (-0.68%)	⬇️

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

Impacted Files	Coverage Δ
superset/db_engines/hive.py	0.00% <0.00%> (-85.72%)	⬇️
superset/db_engine_specs/hive.py	53.90% <0.00%> (-30.08%)	⬇️
superset/db_engine_specs/presto.py	69.76% <0.00%> (-12.32%)	⬇️
superset/examples/world_bank.py	97.10% <0.00%> (-2.90%)	⬇️
superset/examples/birth_names.py	97.59% <0.00%> (-2.41%)	⬇️
superset/views/database/mixins.py	80.70% <0.00%> (-1.76%)	⬇️
superset/models/core.py	87.56% <0.00%> (-0.83%)	⬇️
superset/connectors/sqla/models.py	89.60% <0.00%> (-0.14%)	⬇️
...et-frontend/src/explore/controlPanels/sections.jsx
...t-frontend/src/dashboard/reducers/sliceEntities.js
... and 436 more

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