[Datasource Editor] A few small UI changes in modal to prevent accidental edits

[graceguo-supercat]

CATEGORY

Choose one

• Bug Fix
• Enhancement (new features, refinement)
• Refactor
• Add tests
• Build / Development Environment
• Documentation

SUMMARY

In airbnb there are a few users reported that they accidentally edit datasources, but their original ideal is just change datasource. But it caused other charts that used the datasource became invalid.

1. Don't open the Datasource Editor modal on clicking the data source name. Several people have accidentally edited the datasource when they really mean to change (swap) datasources. Now will show change datasources modal:  

2. Change the order of options in the drop-down menu so that "Change datasource" is the first option (instead of Edit Datasource). Similar reasoning to the above; we want to prioritize Change Datasource over Edit Datasource.

Before:

After:

3. Land the user on the Metrics tab when they get to the Edit Datasource modal (instead of Settings). Adding Metrics is likely the most common reason people would want to edit the datasource from the Explore view. It makes it easier for people to do the most frequent action, and moves people away from the Settings which is the most risky and the least frequent use case.

4. Add a warning to the Settings tab (that is always there) that communicates that changes to this could break all charts, not just your own, so be careful. e.g. "Be careful. Changes to these settings can break all charts, including charts owned by other people."

TEST PLAN

CI and manual tests.

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

REVIEWERS

@michellethomas @etr2460 @mistercrunch

[codecov-io]

Codecov Report

Merging #8471 into master will increase coverage by 0.15%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #8471      +/-   ##
==========================================
+ Coverage   66.41%   66.57%   +0.15%     
==========================================
  Files         449      449              
  Lines       22567    22567              
  Branches     2367     2367              
==========================================
+ Hits        14987    15023      +36     
+ Misses       7442     7406      -36     
  Partials      138      138

Impacted Files	Coverage Δ
.../explore/components/controls/DatasourceControl.jsx	68.75% <ø> (ø)	⬆️
...uperset/assets/src/datasource/DatasourceEditor.jsx	63.39% <100%> (+1.3%)	⬆️
superset/views/core.py	72.15% <0%> (+0.21%)	⬆️
superset/models/core.py	81.46% <0%> (+0.62%)	⬆️
superset/dataframe.py	94.48% <0%> (+1.57%)	⬆️
superset/db_engine_specs/mysql.py	92.15% <0%> (+49.01%)	⬆️

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