New PostgresConnection connect API

[fabianfett]

Motivation

Our current connection creation API is very weird. Adopters first need to connect to a server and then manually call authenticate on the just created connection to auth and select the database.

Changes

• Add new connect method that allows users to connect and auth with a single call
• Add new connect async/await API

Result

Easier to use public interface

Open questions:

• Parameter order in new connect method.
• Splitting up PostgresConnection.Configuration into three subtypes.

[codecov-commenter]

Codecov Report

Merging #245 (8a1abf4) into main (3212037) will increase coverage by 4.13%.
The diff coverage is 48.83%.

@@            Coverage Diff             @@
##             main     #245      +/-   ##
==========================================
+ Coverage   39.57%   43.70%   +4.13%     
==========================================
  Files         115      115              
  Lines        9479     9504      +25     
==========================================
+ Hits         3751     4154     +403     
+ Misses       5728     5350     -378     

Flag	Coverage Δ
unittests	43.70% <48.83%> (+4.13%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...es/PostgresNIO/Connection/PostgresConnection.swift	15.42% <46.34%> (+4.33%)	⬆️
Sources/PostgresNIO/New/PSQLChannelHandler.swift	61.83% <100.00%> (+10.66%)	⬆️
...ces/PostgresNIO/New/PostgresRow-multi-decode.swift	4.44% <0.00%> (+0.19%)	⬆️
Sources/PostgresNIO/Data/PostgresRow.swift	50.00% <0.00%> (+1.02%)	⬆️
...s/PostgresNIO/New/Data/Array+PostgresCodable.swift	94.73% <0.00%> (+1.05%)	⬆️
...rces/PostgresNIO/New/Extensions/Logging+PSQL.swift	19.60% <0.00%> (+1.42%)	⬆️
...ostgresNIO/Deprecated/PostgresMessageDecoder.swift	95.45% <0.00%> (+2.27%)	⬆️
...es/PostgresNIO/New/PSQLBackendMessageDecoder.swift	93.28% <0.00%> (+2.98%)	⬆️
...urces/PostgresNIO/New/Messages/ErrorResponse.swift	32.30% <0.00%> (+3.07%)	⬆️
... and 22 more

[dnadoba]

LGTM

[gwynne]

LGTM!