fix: update pluginSlot to use sandbox base URL

[jsnwesson]

• this PR will update the PluggableDashPOC's PluginSlot dummy config in PluginSlot.jsx to use the sandbox URL.

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (38566b6) 96.08% compared to head (dd7fe44) 96.08%.
Report is 1 commits behind head on aperture/PluggableDashPOC.

Additional details and impacted files

@@                    Coverage Diff                     @@
##           aperture/PluggableDashPOC     #223   +/-   ##
==========================================================
  Coverage                      96.08%   96.08%           
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  Files                            195      195           
  Lines                           1839     1839           
  Branches                         322      322           
==========================================================
  Hits                            1767     1767           
  Misses                            67       67           
  Partials                           5        5           

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