FE: Add Banner to Vet Center FE query and template

[davidmpickett]

User Story or Problem Statement

Follows #18924

User Story

As a veteran, beneficiary or caretaker, I would like to have a banner image displayed at the top of VetCenter facility pages for visual effect.

Description

Implement a GraphQL query to fetch Banner field content and use the existing "Alert" component from the design system to display it on the Vet Center pages.

Figma Designs

Change Management

Ticket: #19363

ACs:

1. Banner exists at the top of VetCenter facility pages
2. Pulls through sample Drupal content from a Vet Center node correctly
3. Must use the ALert component from the DS

### Tasks
- [ ] Write a GraphQL query to fetch the Vet Center Banner field content, with Drupal support.
- [ ] Integrate the ["Alert" component](https://design.va.gov/components/summary-box) to into the template

### QA
- [ ] Verify that the "Alert" component is used for the banner content
- [ ] Verify that the content is correct in the front-end and matches Drupal test data
- [ ] Verify that the alert is displayed correctly and consistently across all Vet Center pages and breakpoints
- [ ] Accessibility Review
- [ ] Design Review

[jilladams]

We can't build this til we decide whether these changes are going into content-build (and creating drift with the AP vet center template) or will be done when we migrate Vet Centers to AP and built in the AP template.