Secondary navigation component refinements

[natalia-fitzgerald]

Description

The purpose of this issue is to refine the secondary navigation component to add the mobile styling. We will model the styling on the cf.gov implementation.

Changes requested

• Add the mobile secondary navigation
  • Example: https://www.consumerfinance.gov/data-research/consumer-credit-trends/auto-loans/
• Extend left sidebar divider line to the bottom of the content area (flex grow?)
  • Divider line should reach the bottom of the content area (For example, when related cases are expanded or collapsed)

[natalia-fitzgerald]

We are working on these fixes as a part of this PR: #560