Support additional connection parameters

[fabianfett]

Fixes: #320.

@jefflewis can you please check if this fixes your use-case?

[codecov-commenter]

Codecov Report

Merging #361 (72d06bf) into main (e60e495) will increase coverage by 0.11%.
The diff coverage is 91.66%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #361      +/-   ##
==========================================
+ Coverage   59.81%   59.93%   +0.11%     
==========================================
  Files         124      124              
  Lines        9915     9937      +22     
==========================================
+ Hits         5931     5956      +25     
+ Misses       3984     3981       -3     

Files	Coverage Δ
.../Connection/PostgresConnection+Configuration.swift	50.00% <100.00%> (+0.70%)	⬆️
...urces/PostgresNIO/New/PostgresChannelHandler.swift	84.77% <100.00%> (ø)
...stgresNIO/New/PostgresFrontendMessageEncoder.swift	100.00% <100.00%> (ø)
...nection State Machine/ConnectionStateMachine.swift	62.87% <86.66%> (+0.41%)	⬆️

... and 3 files with indirect coverage changes