Make feedwitness able to serve metrics

[AlCutter]

No description provided.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 20.50%. Comparing base (3c58af4) to head (d41449c).
⚠️ Report is 217 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/feedwitness/main.go	0.00%	12 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (3c58af4) and HEAD (d41449c). Click for more details.

HEAD has 2 uploads less than BASE

Flag	BASE (3c58af4)	HEAD (d41449c)
	4	2

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #405       +/-   ##
===========================================
- Coverage   51.05%   20.50%   -30.55%     
===========================================
  Files          11       27       +16     
  Lines         903     2048     +1145     
===========================================
- Hits          461      420       -41     
- Misses        374     1567     +1193     
+ Partials       68       61        -7     

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[roger2hk]

Do we need to gracefully shutdown the HTTP server when the application is terminated?

[AlCutter]

Good question - I don't think it matters all that much for this, can come back and add it later if it turns out I'm wrong, though.