Proposal: Standardize field names for HTTP Logging Transport

The HTTP Logging Transport introduced in #1006 (and documented in #1011) is a great addition. However, the field names are not consistent.

For example, for certain request fields, the log field has a name in the format `tf_http_`, such as the requested URI is `tf_http_req_uri`, and the HTTP method is `tf_http_req_method`. However, most header fields are added as-is to the log fields, for example `Accept-Encoding` and `User-Agent`.

I propose using consistent log field naming, for example based on the [Semantic Conventions from OpenTelemetry](https://opentelemetry.io/docs/reference/specification/trace/semantic_conventions/http/).

This would use `http.method` for the request method and `http.url` for the requested URI. Headers are added using a consistent format: `http.[request|response].header.`, where `` is the normalized header name, in lower case, with `-` replaced with `_`. For example, `Accept-Encoding` would be `http.request.header.accept_encoding`.

Start by reading the HTTP Logging Transport introduced in #1006 and its documentation in #1011, then compare its current request, response, and header field names with the linked OpenTelemetry semantic conventions. Done means the transport uses a consistent naming scheme, including normalized request and response header fields, with the intended behavior documented.

Written by the indexing model from the issue text.