[Instrumentation.AWSLambda] Update to net6.0

[martincostello]

Contributes to #1523.

Changes

Spun off from #1544.

Target net6.0 instead of netstandard2.0 as AWS Lambda no longer supports versions of .NET less than .NET 6.

• Appropriate CHANGELOG.md updated for non-trivial changes

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (71655ce) 73.91% compared to head (b99dc5a) 80.58%.
Report is 120 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1545      +/-   ##
==========================================
+ Coverage   73.91%   80.58%   +6.67%     
==========================================
  Files         267      113     -154     
  Lines        9615     3055    -6560     
==========================================
- Hits         7107     2462    -4645     
+ Misses       2508      593    -1915     

Flag	Coverage Δ
unittests-Solution	80.58% <88.57%> (?)

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

Files	Coverage Δ
...Telemetry.Exporter.InfluxDB/InfluxDBEventSource.cs	60.00% <ø> (ø)
...ry.Exporter.InfluxDB/InfluxDBExporterExtensions.cs	100.00% <100.00%> (ø)
...metry.Exporter.InfluxDB/InfluxDBMetricsExporter.cs	84.61% <ø> (-3.85%)	⬇️
...Telemetry.Exporter.InfluxDB/PointDataExtensions.cs	87.50% <100.00%> (ø)
...ry.Exporter.InfluxDB/TelegrafPrometheusWriterV1.cs	100.00% <ø> (ø)
...ry.Exporter.InfluxDB/TelegrafPrometheusWriterV2.cs	100.00% <ø> (ø)
...stana/Implementation/InstanaExporterEventSource.cs	0.00% <ø> (ø)
...try.Exporter.Instana/Implementation/InstanaSpan.cs	100.00% <ø> (ø)
...orter.Instana/Implementation/InstanaSpanFactory.cs	100.00% <ø> (ø)
...er.Instana/Implementation/InstanaSpanSerializer.cs	93.79% <ø> (ø)
... and 32 more

... and 224 files with indirect coverage changes