Workflow pages: shareable forms that start workflows

**What the feature is (as Title)**

Workflow pages: shareable forms that start workflows

**Value proposition**

Many automations begin with a request from someone who will never open Kibana. Workflow pages render a workflow's input schema as a hosted, shareable web page, so anyone with the URL can submit input that starts a workflow, no Kibana login required. This unlocks intake and self-service use cases where the requester is outside the operating team.

**Expected outcome**

- A hosted, shareable page generated from a workflow's input schema
- Submissions start the workflow with the provided input
- Intake and self-service scenarios without requiring Kibana access for requesters