Set ECS fields from message templates

[Mpdreamz]

This allows most ECS fields to be set directly from message templates
e.g

Log.Info("{TraceId}", "x"); 

will override trace.id and not assign metadata.TraceId to x.

This only supports ECS fields not part of an array as documented by LogTemplateProperties.*

This contains two breaking changes.

1. Unknown properties no longer ALL go to _metadata.
   If the unknown property is a string or boolean it will be set to the more appropriate labels.* ECS field.
   See: https://github.com/elastic/ecs-dotnet/pull/229/files#diff-c8cee7db06f2fb88e3d446bba43979c060043f289cb18273985dce0a907f0d22R31
2. Known ECS fields in message template properties now directly assign to the appropriate ECS fields if the type matches. Otherwise it will fallback to assigning to labels.* or _metadata.*

[apmmachine]

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• Start Time: 2023-01-16T14:41:29.672+0000

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