Dropdown documentation: Improve example for filters

[silvalaura]

Our Dropdown filter example is hidden within Dropdown with Form. We should add a section under the dropdown documentation that specifically calls out Dropdown Filters.

We'll want to improve both the api and design documentation for this.

Examples:

• Show a complex example with multiple components
• Show an example with a simple filtering system

[silvalaura]

@orion-cengage share your thoughts on how to do this pls