Backend: Use CI/CD UI variables to define parallelism

Update

See #11549 (comment 2692859329)

Problem

The number of desired parallel jobs is oftentimes calculated using a script, As a user, I would like to automatically define that number as the number of parallel jobs instead of configuring it manually each time

Proposal

To reduce the manual intervention can support variable expansion in parallel so users could automatically calculate and update the number of parallel jobs

Drupal 8 Audits:
  stage: Run Audits
  parallel: ${D8_PARALLEL_JOBS}
...

Original ask

We are trying to define variables using the UI to control the number of parallel streams for our CI runs.

CI Lint can't seem to parse the variables correctly as integer type and consequently fails at the first hurdle.

Drupal 8 Audits:
  stage: Run Audits
  parallel: ${D8_PARALLEL_JOBS}
...
Status: syntax is incorrect 
Error: jobs:drupal 8 audits parallel is not a number

Is there a way to be able to pass the parallelism in as a variable?