OTLP LogExporter to support ILogger Scopes

[cijothomas]

Towards : #2482
Focused on just getting the functionality and example usage.
Tests are not added, as the current test approach cannot be used for scopes, so this will be a separate PR.

Open qn:
For scopes, keys are prefixed with "[Scope.depth]:". This does require string allocated, but avoids collision when same keys are repeated in diff. scope depths... We can revisit this based on user feedback :)

For the code below:

            using (logger.BeginScope("My scope 1 with {food} and {color}", "apple", "green"))
            using (logger.BeginScope("My scope 2 with {food} and {color}", "banana", "yellow"))
            {
                logger.LogInformation("Hello from {name} {price}.", "tomato", 2.99);
            }

Sample output from OTLP collector

LogRecord #0
Timestamp: 2022-04-21 18:52:28.8868154 +0000 UTC
Severity: Information
ShortName:
Body: Hello from tomato 2.99.
Attributes:
     -> name: STRING(tomato)
     -> price: DOUBLE(2.99)
     -> {OriginalFormat}: STRING(Hello from {name} {price}.)
     -> [Scope.0]:food: STRING(apple)
     -> [Scope.0]:color: STRING(green)
     -> [Scope.0]:{OriginalFormat}: STRING(My scope 1 with {food} and {color})
     -> [Scope.1]:food: STRING(banana)
     -> [Scope.1]:color: STRING(yellow)
     -> [Scope.1]:{OriginalFormat}: STRING(My scope 2 with {food} and {color})

[codecov]

Codecov Report

Merging #3218 (33db1ae) into main (60f743a) will decrease coverage by 0.50%.
The diff coverage is 25.00%.

@@            Coverage Diff             @@
##             main    #3218      +/-   ##
==========================================
- Coverage   85.74%   85.23%   -0.51%     
==========================================
  Files         260      252       -8     
  Lines        9358     9234     -124     
==========================================
- Hits         8024     7871     -153     
- Misses       1334     1363      +29     

Impacted Files	Coverage Δ
...etryProtocol/Implementation/LogRecordExtensions.cs	87.65% <25.00%> (-6.87%)	⬇️
....TelemetryHttpModule/TelemetryHttpModuleOptions.cs	0.00% <0.00%> (-90.00%)	⬇️
...entation/ExportClient/OtlpGrpcTraceExportClient.cs	35.71% <0.00%> (-42.86%)	⬇️
...xporter.OpenTelemetryProtocol/OtlpTraceExporter.cs	36.36% <0.00%> (-40.91%)	⬇️
...emetry.Api/Internal/OpenTelemetryApiEventSource.cs	76.47% <0.00%> (-5.89%)	⬇️
....AspNet.TelemetryHttpModule/TelemetryHttpModule.cs	0.00% <0.00%> (-5.27%)	⬇️
...ter.ZPages/Implementation/ZPagesActivityTracker.cs	97.14% <0.00%> (-2.86%)	⬇️
...metryProtocol/Implementation/ActivityExtensions.cs	88.73% <0.00%> (-2.71%)	⬇️
...nTelemetry.Instrumentation.AspNet/AspNetMetrics.cs
...Implementation/AspNetInstrumentationEventSource.cs
... and 6 more

[CodeBlanch]

I anticipate users wanting to change this prefix behavior, but something we can tackle later 😄

[reyang]

Might be nice to avoid the new string allocation each time, doesn't block this PR though.

[cijothomas]

Yes. The description has this left as open question.
Merging to make progress. (OTLP Log Exporter is now almost ready feature-wise, except the SDK level issue related to buffering : #2905)

[CodeBlanch]

LGTM