docs: Adhoc Workflow Documentation

[stanbrub]

• Documented what an Adhoc Workflow is and the two types
• Documented how to run each Adhoc Workflow
• Documented how to run an Adhoc Dashboard

For reviewers:

• Start with the README from the PR branch
• The Concepts Guide has already been reviewed but was moved
• Since you likely don't have the secrets for the Adhoc Existing workflow, you'll can't test that
• The assumption is that you already have the permissions to run the Adhoc Auto-provisioned action from main
• Both of these workflows have been used in practice dozens of times, so the review is mostly whether or not the instructions make sense