[Feature]: Shiny App NavBar

[jimbrig]

The DataHub Shiny App's UI will be created using bslib and the main page built via bslib::page_navbar().

This issue pertains to the navigation of the application via bslib's navbar based navigation (as opposed to sidebar-based navigation like used in shinydashboard / AdminLTE based frameworks).

• Design navigation structure for the app
• Implement primary sections (i.e. Home, Data Views, Reports, Summary)
• Style and position navbar to match overall theme

NavBar Components:

• Title: "brand" with the GMH logo properly sized and responsive
• Navigation: Navigation for the app will leverage bslib::nav_panel() and bslib::nav_menu() primarilly
• Theme: Custom bslib::bs_theme(version = 5, ...) styles and variables
• Sidebar: (separate issue)