UX design pattern: SDK readiness page header

Create a standard page header template that matches the API readiness screens.

**Success criteria**
- Design pattern is scalable and can be applied across other apps to create a coherent experience for service partners.
- Design pattern is pressure-tested for accessibility, color, and usability.
- Design pattern reuses common Fluent components.
- Design pattern contains the following fields: **Target date: YYYY-MM-DD**, **API spec: ``**

**Tasks**

- [x] Create lo-fi designs for review
- [ ] Refine design
- [ ] Hand-off for implementation