BCDA-7973: Add loading for Try The API creds

[austincanada]

Add "dynamic" loading for Try The API code snippets. Puts test credentials into YML file which can be used for the rest of the codebase or other credentials.

🎫 Ticket

https://jira.cms.gov/browse/BCDA-7973

🛠 Changes

(What was added, updated, or removed in this PR.)
Added YML file to hold sandbox clients and secrets.
Updated existing usages of hard-coded clients and secrets to pull from YML file.

ℹ️ Context for reviewers

N/A

✅ Acceptance Validation

Viewed changes within local environment.

🔒 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.

[alex-dzeda]

I think this will be ready to go once screenshots of the site (eg the credentials) with the changes attached (after merging changes upstream from main) are added to AC! Good job