Add note on updating sandbox cluster configuration

[jeevb]

Describe your changes

Adds notes on updating and reloading Flyte sandbox cluster configuration.

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (64f097f) 59.40% compared to head (934d1d0) 59.40%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4510   +/-   ##
=======================================
  Coverage   59.40%   59.40%           
=======================================
  Files         638      638           
  Lines       53957    53957           
=======================================
  Hits        32052    32052           
  Misses      19376    19376           
  Partials     2529     2529           

Flag	Coverage Δ
unittests	59.40% <ø> (ø)

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