chore: optional ts type of onDemand

[ClarkXia]

server.onDemand is optional.

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (release/next@18ea5b2). Click here to learn what that means.
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@               Coverage Diff               @@
##             release/next    #6010   +/-   ##
===============================================
  Coverage                ?   81.94%           
===============================================
  Files                   ?      197           
  Lines                   ?    18104           
  Branches                ?     2356           
===============================================
  Hits                    ?    14836           
  Misses                  ?     3233           
  Partials                ?       35           

Impacted Files	Coverage Δ
packages/ice/src/types/userConfig.ts	100.00% <100.00%> (ø)

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