bin/monitor: Convert to async

[Turbo87]

This (partially) removes the need for us to use a blocking reqwest client, which will be refactored in a follow-up PR.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 38 lines in your changes missing coverage. Please review.

Project coverage is 89.03%. Comparing base (828f52e) to head (9888fd1).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
src/bin/monitor.rs	0.00%	28 Missing ⚠️
src/db.rs	0.00%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9578      +/-   ##
==========================================
- Coverage   89.10%   89.03%   -0.07%     
==========================================
  Files         289      289              
  Lines       29057    29076      +19     
==========================================
- Hits        25890    25888       -2     
- Misses       3167     3188      +21     

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