feat(lcs-factory) : add utility function to choose N closest contact pairs

[Meow404]

fixes #32

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This change is 

[github-actions]

LCOV of commit 5fded9a during C3 Coverage #77

Summary coverage rate:
  lines......: 91.9% (1467 of 1597 lines)
  functions..: 77.5% (131 of 169 functions)
  branches...: 52.0% (1224 of 2356 branches)

Files changed coverage rate:
                                        |Lines       |Functions  |Branches    
  Filename                              |Rate     Num|Rate    Num|Rate     Num
  ============================================================================
  multibody/lcs_factory.cc              | 4.8%    335|3725%    16|    -      0
  multibody/lcs_factory.h               |33.3%      3|1200%     1|    -      0
  multibody/lcs_factory_options.h       | 6.7%     30| 800%     2|    -      0