Add timeline component to pattern library (created for Building Housing)

[reillyzlab]

A timeline component was designed and created for boston.gov/buildinghousing section the website.

This should be converted to a global component available in patterns and then in Drupal (i.e. boston.gov)

Design files are here: https://drive.google.com/drive/folders/1m5hNXS8b6d-CT2DukVfbPpL5o5dSC_0m as well as shared with @sebastianebarb @matthewcrist @subaha-cob

Example: https://www.boston.gov/buildinghousing/holborn-street-neighborhood-homes + attached screenshots

[reillyzlab]

Related item to resolve as part of this:

• Remove additional padding from text updates boston.gov-d8#1990
• Write alt text for all icons to ensure accessibility in timeline navigation boston.gov-d8#1853

Potentially also related: CityOfBoston/boston.gov-d8#1886