Add validation step in workflow submission / scheduling

[mvdbeek]

To make sure we catch things as early as possible.
xref #7781 (comment)

[mvdbeek]

e.g. https://sentry.galaxyproject.org/organizations/galaxy/issues/215647/events/5e3f1b3f36b34201ae75dae4b804a9ad/ where workflow text parameter received an integer via planemo run.