Correctly place the SSL channel handler in front of the PostgresChannelHandler

[tkrajacic]

Ensure that NIOSSLClientHandler is added immediately before PostgresChannelHandler instead of at the front of the entire pipeline.
This ensures that TLS works correctly when working with preexisting channels, such as tunneling connections with NIOSSH. See also #526 .

Thanks to @Joannis and @gwynne for finding the problem and pointing me to the right place to fix it.

[fabianfett]

Great patch! See comments. Pretty sure you will need to fix some tests.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 61.76%. Comparing base (f2a6394) to head (0e648c1).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...es/PostgresNIO/Connection/PostgresConnection.swift	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #527      +/-   ##
==========================================
- Coverage   61.77%   61.76%   -0.01%     
==========================================
  Files         125      125              
  Lines       10072    10072              
==========================================
- Hits         6222     6221       -1     
- Misses       3850     3851       +1     

Files with missing lines	Coverage Δ
...urces/PostgresNIO/New/PostgresChannelHandler.swift	84.50% <100.00%> (ø)
...es/PostgresNIO/Connection/PostgresConnection.swift	42.75% <33.33%> (ø)

... and 1 file with indirect coverage changes

[fabianfett]

Great patch! Thanks!