Accordion: Add actions slot and list view variant

[twjeffery]

Description

The accordion component doesn't support right-aligned actions (buttons, links) in the header row. In workspace list views, each expandable row needs actions on the right (e.g., comments link, View button), but there's no slot for this.

Without an actions slot to have an expanding list view in our tables, we currently need to build custom expandable list components that duplicate accordion behavior.

<GoabAccordion heading="Client Name">
  <span slot="headingcontent">
    <GoabBadge type="success" content="Active" />
  </span>
  <span slot="actions">
    <GoabLink leadingIcon="chatbox">5 comments</GoabLink>
    <GoabButton type="tertiary" size="compact">View</GoabButton>
  </span>
</GoabAccordion>

List view variant

A variant for list view usage where the header has a filled background with hover:

• Default background: greyscale-100
• Hover background: greyscale-150

This matches the pattern where each row has a subtle grey header that darkens on hover to indicate interactivity.

Screenshots

Acceptance Criteria

1. New type property with options "normal", "filled"
2. Modify Accordion so any interactive options inside headingContent don't trigger Accordion
3. Investigate using headingContent slot for right aligned actions
   • Involve Tom to decide if that's what we want

[ArakTaiRoth]

@twjeffery Take a look into the option names and decide what you want