feat: show user email in dashboard API

[betodealmeida]

SUMMARY

I added the user email to the response from the dashboard API (we already return username, first and last name). This is need to sync dashboards to DBT exposures, since it requires the email of the dashboard owner.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N/A

TESTING INSTRUCTIONS

Check the response from /api/v1/dashboard/, it should have the email of the owners.

I updated the unit test.

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 #19004 (425cec0) into master (19eb73b) will decrease coverage by 14.46%.
The diff coverage is n/a.

❗ Current head 425cec0 differs from pull request most recent head 9906294. Consider uploading reports for the commit 9906294 to get more accurate results

@@             Coverage Diff             @@
##           master   #19004       +/-   ##
===========================================
- Coverage   66.58%   52.12%   -14.47%     
===========================================
  Files        1641     1641               
  Lines       63548    63548               
  Branches     6424     6424               
===========================================
- Hits        42315    33122     -9193     
- Misses      19554    28747     +9193     
  Partials     1679     1679               

Flag	Coverage Δ
hive	52.61% <ø> (ø)
javascript	51.38% <ø> (ø)
mysql	?
postgres	?
presto	52.45% <ø> (ø)
python	52.88% <ø> (-29.43%)	⬇️
sqlite	?

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

Impacted Files	Coverage Δ
superset/dashboards/api.py	48.81% <ø> (-43.73%)	⬇️
superset/tables/schemas.py	0.00% <0.00%> (-100.00%)	⬇️
superset/columns/schemas.py	0.00% <0.00%> (-100.00%)	⬇️
superset/utils/dashboard_import_export.py	0.00% <0.00%> (-100.00%)	⬇️
superset/utils/pandas_postprocessing/boxplot.py	22.22% <0.00%> (-77.78%)	⬇️
superset/dashboards/commands/importers/v0.py	14.79% <0.00%> (-75.15%)	⬇️
superset/utils/pandas_postprocessing/rolling.py	17.50% <0.00%> (-75.00%)	⬇️
superset/tasks/alerts/observer.py	27.77% <0.00%> (-72.23%)	⬇️
superset/databases/commands/importers/v1/utils.py	27.77% <0.00%> (-72.23%)	⬇️
superset/datasets/commands/importers/v0.py	24.82% <0.00%> (-68.80%)	⬇️
... and 283 more

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[lilykuang]

code LGTM. please fix the tests before merge :)