Start log lines with the Lambda request ID

[mnapoli]

Closes #3

Application logs had no Lambda request ID, so an error logged by the application could not be tied to its invocation: not to Bref's own lines (timeouts, Invoke Error), not to Lambda's REPORT line (duration, memory), and not to the other logs of the same request.

When $_SERVER['LAMBDA_REQUEST_ID'] is set (by Bref, on every invocation), StderrLogger now starts each line with it, like the logs of Lambda's native runtimes. This is the approach explored in #3:

8f507cfc-8b35-4e7e-9f26-f2a3a6e7e1a2	INFO	This is an info	{"message":"This is an info","level":"INFO"}

This is the same change as brefphp/monolog-bridge#2 for Bref's Monolog formatter (tested there on AWS with PHP-FPM, Octane, a queue worker and console commands). PHP-FPM needs brefphp/bref#2189.