optionally return additional arguments from `lqr` and `kalman`

[baggepinnen]

[JuliaControlBot]

This is an automated message. Plots were compared to references. 4/11 images have changed, see differences below. After pulling this PR, please update the reference images by creating a PR to ControlExamplePlots.jl here.

Difference	Reference Image	New Image
:heavy_check_mark: 0.0
:heavy_check_mark: 0.0
:heavy_check_mark: 0.008
:heavy_check_mark: 0.0

[franckgaga]

Just notice this PR and +1 for this feature, it would be useful for me!

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 92.35%. Comparing base (64a7974) to head (fd32ae0). :warning: Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #994   +/-   ##
=======================================
  Coverage   92.34%   92.35%           
=======================================
  Files          41       41           
  Lines        5150     5155    +5     
=======================================
+ Hits         4756     4761    +5     
  Misses        394      394           

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