Investigate middleware to perform gzencode for error reporting

[asgrim]

#243 (comment)

scout-apm-php/src/Errors/ScoutClient/CompressPayload.php

Lines 14 to 17 in 676fd85

	public function __invoke(string $payload): string
	{
	return gzencode($payload);
	}

shouldn't the HTTP client do this for us?

#243 (comment)

scout-apm-php/src/Errors/ScoutClient/HttpErrorReportingClient.php

Line 137 in 676fd85

->withHeader('Content-Encoding', 'gzip') // Must be gzipped

could it be handled by a middleware?

See if the above could be improved?