BCDA-7844: Update the Data Dictionary with plain language

[greg-pf]

🎫 Ticket

https://jira.cms.gov/browse/BCDA-7844

🛠 Changes

Updated the data dictionary with plain language and other accessibility improvements

ℹ️ Context for reviewers

Drafted and reviewed the content changes in the data dictionary with Eric, Jennifer, Natalie, and Karley. The data dictionary updates were approved in BCDA-7844

✅ Acceptance Validation

Testing done in staging and compared to production
Confirmed the correct file is downloaded in staging

Existing:

• production: https://bcda.cms.gov/data.html#bcda-data-dictionary
• 

Proposed

• staging: https://stage.bcda.cms.gov/data.html#bcda-data-dictionary
• 

🔒 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.