Update protos to v0.19.0

[alanwest]

With the addition of option csharp_namespace = "OpenTelemetry.Proto.* to the proto files in v0.19.0 I find the namespaces much more soothing to the 👀.

[codecov]

Codecov Report

Merging #3535 (e860388) into main (21d185a) will decrease coverage by 0.27%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #3535      +/-   ##
==========================================
- Coverage   86.82%   86.55%   -0.28%     
==========================================
  Files         275      275              
  Lines        9949     9949              
==========================================
- Hits         8638     8611      -27     
- Misses       1311     1338      +27     

Impacted Files	Coverage Δ
...metryProtocol/Implementation/ActivityExtensions.cs	91.20% <ø> (-3.30%)	⬇️
...ementation/ExportClient/OtlpGrpcLogExportClient.cs	78.57% <ø> (ø)
...tation/ExportClient/OtlpGrpcMetricsExportClient.cs	78.57% <ø> (ø)
...entation/ExportClient/OtlpGrpcTraceExportClient.cs	35.71% <ø> (-42.86%)	⬇️
...ementation/ExportClient/OtlpHttpLogExportClient.cs	0.00% <ø> (ø)
...tation/ExportClient/OtlpHttpMetricsExportClient.cs	62.50% <ø> (ø)
...entation/ExportClient/OtlpHttpTraceExportClient.cs	87.50% <ø> (ø)
...etryProtocol/Implementation/LogRecordExtensions.cs	87.95% <ø> (ø)
...tryProtocol/Implementation/MetricItemExtensions.cs	93.83% <ø> (ø)
...Protocol/Implementation/OtlpKeyValueTransformer.cs	85.71% <ø> (ø)
... and 12 more