Add opensbx postman collection for website/customer testing.

[laurenkrugen-navapbc]

🎫 Ticket

https://jira.cms.gov/browse/BCDA-xxx

🛠 Changes

added a postman collection that contains BCDA API endpoints and basic setup for customers to test/try.

ℹ️ Context for reviewers

BCDA doesn't have a postman collection available to try on the website.

✅ Acceptance Validation

built/tested in postman.

🔒 Security Implications

• This PR adds a new software dependency or dependencies.
• This PR modifies or invalidates one or more of our security controls.
• This PR stores or transmits data that was not stored or transmitted before.
• This PR requires additional review of its security implications for other reasons.

If any security implications apply, add Jason Ashbaugh (GitHub username: StewGoin) as a reviewer and do not merge this PR without his approval.