feature: conditionals for Argo Workflows

[saikonen]

Adds Conditional support to Argo Workflows

TODO:

• nesting a conditional as the last step inside a foreach is not yet working. This is now out of scope for the initial release
• test @parallel with conditionals
• test regular flows with argo for possible regressions

Open issues to solve in another PR:

• conditionals as last step in a foreach. requires thorough input-paths rework
• @parallel as a switch step, where it leads to more than one possible parallel-join step. This needs to either be fixed, or blocked. Issue exists with local conditional runs as well so outside of the scope for this PR