Backport of Remove wrong VariableFlags parameter from parse job endpoint into release/1.8.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #23909 to be assessed for backporting due to the inclusion of the label backport/1.8.x.

🚨

Warning automatic cherry-pick of commits failed. If the first commit failed,
you will see a blank no-op commit below. If at least one commit succeeded, you
will see the cherry-picked commits up to, not including, the commit where
the merge conflict occurred.

The person who merged in the original PR is:
@Juanadelacuesta
This person should manually cherry-pick the original PR into a new backport PR,
and close this one when the manual backport PR is merged in.

merge conflict error: unable to process merge commit: "4972b7382da24eb81d7eafb7e2cf1b2d1b853dd5", automatic backport requires rebase workflow

The below text is copied from the body of the original PR.

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Currently the documentation for the parse job endpoint mentions the parameter VariableFlags which is not actually supported by the code, this PR removes it from the website.

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Overview of commits

• 4972b73

[hashicorp-cla-app]

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