Background

This is a proposed enhancement to the original task of adding 'On this day' to the feed (see T175995); and dependent on user feedback and enthusiasm for viewing different types of On this day content, especially celebrity births/deaths as being particularly popular/associated with Wikipedia.
Note that endpoint for On this day already supports showing all event types (Births, Deaths, and Observances). However, initially these other event types were omitted due to the relative higher incidence of culturally-specific/obscure births, deaths and observances in the list, as well as the additional work of prepending/appending text strings to present these other event types.

User story

As a fan of reading 'On this day' content, I want to be able to see all types of 'On this day' events.

Proposed solution

Part A. In the details view, provide a a filter component allowing filtering to view all OTD event types

Filter bar with just historical events	Filter bar stays 'pinned' under toolbar on scroll

Design details:

• The filter bar is visible and remains 'pinned' under the toolbar at all times
• The 'dot' element next to the year of an event is replaced with the icon for the event type
• The number of events in the header section changes depending on the event types selected
• Birth type events - prepend the birth event with Birth of, since the event text only shows the name of the person who was born on that day.
• Death type events - prepend the death event with Death of, since the event text only shows the name of the person who died on that day.
• Observance type events - since observances are generally annual event not tied to a particular year, it is proposed that these appear at the top of the list if shown with the name of the event in place of the year as event title.

Part B. Update the On this day card to show one 'featured' event for each type of event

This may be considered as an independent enhancement for consideration dependent on the extent we'd like to promote the other event types on the feed itself, and potentially based on data regarding the interaction rate with the inset article cards on the On this day card.

• The article image used in the inset event card will be the lead image for the most prominent article in the event description, or else show the event type icon where no image is available.
• Birth type events - prepend the birth event with Birth of, since the event text only shows the name of the person who was born on that day.
• Death type events - prepend the death event with Death of, since the event text only shows the name of the person who died on that day.
• Observance type events - since observances are generally annual event not tied to a particular year, it is proposed that these appear at the top of the list if shown with the name of the event in place of the year as event title.