Add cursor pointer to chart expandable labels

[contolini]

Changes the cursor to a pointer on hover to indicate they're clickable.

Changes

• Cursor state when hovering over a chart expandable.

Testing

• Visit https://www.consumerfinance.gov/data-research/consumer-complaints/search/ and scroll down to the row chart and note that the drop-down and text can clicked be to expand the chart, however, neither has any indication they can be clicked.
• If you try it locally with this branch, they should have a cursor pointer on hover.

Screenshots

Notes

Todos

Checklist

• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows the standards laid out in the front end playbook
• Passes all existing automated tests
• New functions include new tests
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged
• Visually tested in supported browsers and devices
• Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)