Fix request header filtering and other improvements

Fixed

• Use case-insensitive comparison when filtering request and response headers (http.request.header.* and http.response.header.* span attributes) using the values in the appsignal.config.request_headers and appsignal.config.response_headers resource attribute configuration options.
• Keep reporting a request's path when the appsignal.config.send_request_query_parameters resource attribute configuration option is set to false. The url.full and http.target span attributes now lose their query string rather than being removed, because they hold the request path as well. Applications whose instrumentation reports the path in http.target, without also reporting an http.route attribute, showed no path on their samples and error incidents.
• Report request and response headers in lowercase and using dashes as separators, following the current OpenTelemetry semantic conventions. The values in the lists of allowed header names in the appsignal.config.request_headers and appsignal.config.response_headers resource attribute configuration options are also normalized to this shape before comparison.

This release can be installed through our collector packages and Docker image.