Add tests for AWS V4 Signer examples

[adam-fowler]

The signer examples can be found here

Add tests for these and fix one minor difference by removing space between items in authorization header

[codecov[bot]]

Codecov Report

Merging #522 (13d0246) into main (f8a8db6) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #522   +/-   ##
=======================================
  Coverage   72.49%   72.49%           
=======================================
  Files          78       78           
  Lines        6134     6134           
=======================================
  Hits         4447     4447           
  Misses       1687     1687           

Impacted Files	Coverage Δ
Sources/SotoSignerV4/signer.swift	90.00% <100.00%> (ø)

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