This adds extensibility to the logging middleware so that what gets logged can be granularly customized per request.

Description

See the API review notes at #31844 (comment)

Fixes #31844, contributes to dotnet/extensions#4330
Fixes #49989, CopyTo/Async not logging the request body.
Fixes #49063, Clarify when the request body is not fully logged.

IHttpLoggingInterceptor:

• This is a new interface that can have multiple instances registered and injected into the logging middleware. The callbacks run before the normal request/response logging and enable adjusting what should be logged per request, as well as adding custom fields.
• ValueTask OnRequestAsync(HttpLoggingInterceptorContext logContext);
• ValueTask OnResponseAsync(HttpLoggingInterceptorContext logContext);

Duration:

• This is a new field that can be logged, reported as milliseconds since the middleware first saw the request. This is logged once at the end of the response.

info: Microsoft.AspNetCore.HttpLogging.HttpLoggingMiddleware[2]
      Response:
      Content-Type: RedactedHeader
      ResponseEnrichment: Stuff
      StatusCode: 200
info: Microsoft.AspNetCore.HttpLogging.HttpLoggingMiddleware[8]
      Duration: 0.3027ms

Combine Logs:
bool HttpLoggingOptions.CombineLogs { get; set; } has been added to support writing one unified log of request, request body, response, and response body data at the end of the response. The extensions components require this.

Exception handling:

• The middleware has been updated to ensure that all data collected so far is logged even in the event of an exception thrown from the middleware pipeline. This is especially important for the new CombineLogs option since the request data won't have been logged before calling next. Note that since this middleware does not handle the exception, it does not log it so as to avoid duplicating it in the logs.