Edit embed field config to allow marking a field as searchable

[jwalgran]

Overview

Edit embed field config to allow marking a field as searchable and add model and API support for persistence.

Describe the solution you'd like

• Model changes
  • Add searchable to EmbedField, non null default False
  • Add text_search_label to EmbedConfig, nullable string
  • Add custom_text to FacilityIndex, nullable string
• Update API to allow passing a searchable value
• Update UI to allow making embed fields as "Searchable"

[TaiWilkin]

Design notes: Use a checkbox to the right of the fields (but before the hidden draggable buttons). Distance between right checkbox and textbox slightly larger than between left checkbox and textbox. Make this disabled and a very pale grey unless a box is marked 'visible'; deselect the checkbox if a box was visible and searchable but is marked invisible. Have a 'header'/label above the list of fields' checkboxes marked 'Searchable' with an 'i' icon; on hover, show instructions/definition for searchability.