Expose the LAMBDA_REQUEST_ID variable in PHP-FPM too

[mnapoli]

The function and console runtimes set LAMBDA_REQUEST_ID on every invocation (#2035), and the docs say Bref sets it on "every Lambda invocation", but PHP-FPM workers only received LAMBDA_INVOCATION_CONTEXT (JSON). This passes LAMBDA_REQUEST_ID to PHP-FPM too, so $_SERVER['LAMBDA_REQUEST_ID'] (and getenv()) works the same in every runtime. Documented in fpm-runtime.mdx. See brefphp/laravel-bridge#145 for users looking for the ID.

That lets Bref's log formatters start every line with the request ID in PHP-FPM too: brefphp/monolog-bridge#2 and brefphp/logger#12. The documentation of the logs of a single request is in #2190.

Tested on AWS with a Laravel application (PHP-FPM, Octane, queue worker, console) using this branch and the monolog-bridge branch. For a PHP-FPM request that timed out, one filter @requestId = '…' query in Logs Insights returns:

START RequestId: 092cf7a5-…
092cf7a5-…	INFO	Starting something slow	{"message":"Starting something slow","level":"INFO"}
092cf7a5-… The PHP script timed out. Bref will now restart PHP-FPM…
092cf7a5-…	Invoke Error	{"errorType":"Bref\\FpmRuntime\\FastCgi\\Timeout",…}
END RequestId: 092cf7a5-…
REPORT RequestId: 092cf7a5-…	Duration: 7056.69 ms	…