Implemented margo_monitor_dump

[mdorier]

This PR adds a margo_monitor_dump function that takes a function pointer and calls it with a serialized representation of the monitor's state. If reset is set to true, this function will also reset to monitor's state.

[codecov]

Codecov Report

Attention: Patch coverage is 92.45283% with 8 lines in your changes are missing coverage. Please review.

Project coverage is 57.41%. Comparing base (08032be) to head (a46e4f7).

Files	Patch %	Lines
src/margo-default-monitoring.c	88.05%	1 Missing and 7 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #273      +/-   ##
==========================================
+ Coverage   57.17%   57.41%   +0.24%     
==========================================
  Files          69       69              
  Lines        9548     9626      +78     
  Branches     1242     1252      +10     
==========================================
+ Hits         5459     5527      +68     
- Misses       3331     3332       +1     
- Partials      758      767       +9     

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