Expose more columns in saved queries API

[betodealmeida]

I've updated SavedQueryAPI to show more columns, including the user's email and the database SQLAlchemy URI. This is in preparation to introducing scheduled queries.

@mistercrunch I could use your input here, is there best practices for changing the views?

[codecov-io]

Codecov Report

Merging #6686 into master will increase coverage by <.01%.
The diff coverage is 60%.

@@            Coverage Diff             @@
##           master    #6686      +/-   ##
==========================================
+ Coverage   56.19%   56.19%   +<.01%     
==========================================
  Files         520      520              
  Lines       23181    23186       +5     
  Branches     2765     2765              
==========================================
+ Hits        13027    13030       +3     
- Misses       9744     9746       +2     
  Partials      410      410

Impacted Files	Coverage Δ
superset/views/sql_lab.py	93.75% <100%> (+0.13%)	⬆️
superset/models/sql_lab.py	95.65% <50%> (-2.81%)	⬇️

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[mistercrunch]

LGTM