feat: load examples from config instead of code

[betodealmeida]

SUMMARY

Currently the examples that come with Superset are all generated by Python scripts, making modifying the existing examples or creating new ones unnecessarily complicated.

With the new export/import functionality from SIP-54 we can store the examples in the repo as YAML files instead of code. This way the examples can be easily modified, and new examples can be created inside Superset, exported and added to the repo.

In this PR I moved the "Unicode test" example to YAML files. Doing so required a few modifications, namely, adding a data attribute to the dataset config pointing to a URL where the data can be download as a CSV. This is similar to how load_examples currently work, with the difference that we don't know the column types a priori, so they need to be inferred from the dataset metadata.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N/A

TEST PLAN

I loaded the examples, and verified that the unicode test is imported and set up correctly.

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

[codecov-io]

Codecov Report

Merging #12026 (a115395) into master (e0079bb) will increase coverage by 0.05%.
The diff coverage is 45.04%.

@@            Coverage Diff             @@
##           master   #12026      +/-   ##
==========================================
+ Coverage   63.72%   63.78%   +0.05%     
==========================================
  Files         956      474     -482     
  Lines       46941    29270   -17671     
  Branches     4589        0    -4589     
==========================================
- Hits        29915    18669   -11246     
+ Misses      16842    10601    -6241     
+ Partials      184        0     -184     

Flag	Coverage Δ
javascript	?
python	63.78% <45.04%> (-0.59%)	⬇️

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

Impacted Files	Coverage Δ
superset/cli.py	34.78% <0.00%> (+0.09%)	⬆️
superset/examples/utils.py	31.57% <31.57%> (ø)
superset/datasets/commands/importers/v1/utils.py	55.93% <39.28%> (-15.04%)	⬇️
superset/commands/importers/v1/examples.py	45.45% <45.45%> (ø)
superset/commands/importers/v1/__init__.py	95.94% <100.00%> (ø)
superset/commands/importers/v1/utils.py	86.11% <100.00%> (ø)
...erset/dashboards/commands/importers/v1/__init__.py	100.00% <100.00%> (ø)
superset/dashboards/commands/importers/v1/utils.py	93.75% <100.00%> (+2.08%)	⬆️
superset/datasets/schemas.py	96.46% <100.00%> (+0.03%)	⬆️
superset/examples/__init__.py	100.00% <100.00%> (ø)
... and 493 more

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[bkyryliuk]

nice improvement !