Add advanced frontpage layout config option

[pixeldesu]

The current frontpage is mostly for "marketing" purposes, displaying all the different features Retrospring has. This isn't really required for self-hosted instances. So this Pull Request adds a by default enabled simple layout.

The configuration option added for this is the following:

features:
  # Advanced (marketing) frontpage layout
  advanced_frontpage:
    enabled: false

Mobile layout	Desktop layout

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.92%. Comparing base (66a1998) to head (784e9e0).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1828   +/-   ##
=======================================
  Coverage   95.91%   95.92%           
=======================================
  Files         180      180           
  Lines        2816     2819    +3     
=======================================
+ Hits         2701     2704    +3     
  Misses        115      115           

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[sentry-io]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ ActionView::MissingTemplate: Missing template about/index_advanced with {:locale=>[:en], :formats=>[:json, :xml, :js], :varian... AboutController#index View Issue

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[nilsding]

ah, sentry errors are because of some bot activities as indicated by the headers:

Accept: application/json, application/xml, text/json, text/x-json, text/javascript, text/xml
User-Agent: RestSharp/1.0.0.0

of course there's no json template for that, silly!