DATAP-1476 Add Aggregation.less stylesheet to SimpleFilter component

[cdmh219]

During conversion of SimpleFilter to functional component, the reference for the Aggregation.less stylesheet was missed, resulting in various styling issues. This needs to be added in to resolve them.

Additions

-Aggregation.less

Removals

Changes

Testing

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)