fix: missing orderby in query on the nvd3 timeseries chart

[zhaoyongjie]

SUMMARY

currently, order by clause must be explicitly selected in the explore control, and cannot send asc query to database.

this PR fixed

• make the first metric as the main metric for implicit orderby column
• ensure asc orderby

Partially fixed #13792

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

after

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• Has associated issue: [chart]Time Series Bar Chart does not sort #13792
• 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 #15343 (89dfcbe) into master (ab153e6) will increase coverage by 0.09%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master   #15343      +/-   ##
==========================================
+ Coverage   77.14%   77.24%   +0.09%     
==========================================
  Files         973      973              
  Lines       50473    50510      +37     
  Branches     6183     6183              
==========================================
+ Hits        38938    39017      +79     
+ Misses      11329    11287      -42     
  Partials      206      206              

Flag	Coverage Δ
hive	81.44% <83.33%> (+0.02%)	⬆️
mysql	81.71% <83.33%> (+0.02%)	⬆️
postgres	81.73% <83.33%> (+0.02%)	⬆️
presto	81.43% <83.33%> (?)
python	82.26% <83.33%> (+0.18%)	⬆️
sqlite	81.36% <83.33%> (+0.02%)	⬆️

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

Impacted Files	Coverage Δ
superset/viz.py	56.52% <66.66%> (+0.05%)	⬆️
superset/utils/core.py	89.09% <100.00%> (+0.04%)	⬆️
superset/views/core.py	75.54% <0.00%> (-0.04%)	⬇️
superset/errors.py	100.00% <0.00%> (ø)
superset/views/sql_lab.py	60.68% <0.00%> (ø)
superset/models/core.py	90.02% <0.00%> (+0.26%)	⬆️
superset/sql_lab.py	83.62% <0.00%> (+1.39%)	⬆️
superset/connectors/sqla/models.py	89.87% <0.00%> (+1.41%)	⬆️
superset/connectors/connector_registry.py	83.33% <0.00%> (+4.64%)	⬆️
superset/db_engine_specs/presto.py	90.31% <0.00%> (+5.89%)	⬆️

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[villebro]

LGTM