Draft: Spike: Explore use of `vars` interpolation option

What does this MR do and why?

Project CI/CD variables:

# unprotected

INTERPOLATION_JOB_NAME: interpolation_var_job
INTERPOLATION_VAR: var interpolation works

CI/CD config files:

# .gitlab-ci.yml

include:
    local: included.yml

# included.yml

$[[ vars.INTERPOLATION_JOB_NAME ]]:
    script: ls

included_job:
    script:
        - echo "$[[ vars.INTERPOLATION_VAR ]]"

Jobs created:

Job output rendering variable value:

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #387632 (closed)