Expose ci job services as custom

What does this MR do?

!1827 (merged) exposed the services as CI_JOB_SERVICES but in the custom executor envs are exported ad CUSTOM_ENV_CI_JOB_SERVICES.

Why was this MR needed?

To have CI_JOB_SERVICES more in line with other custom executor env variables

What's the best way to test this MR?

A custom executor with:

run_exec = "path/to/script.sh"

script.sh

#!/bin/bash

echo HI
echo $CUSTOM_ENV_CI_JOB_SERVICES

What are the relevant issue numbers?

#4358 (closed)