Generate user_friendly examples if it states true or false in examples

[ESapenaVentura]

User story

• As a DCP Data wrangler and part of the metadata schema team
• I want to show user friendly values for boolean fields
• so that contributors that have to fill the spreadsheet know they can fill boolean fields with "yes" and "no"

This user story is related to a pending schema change HumanCellAtlas/metadata-schema#1397 . The schema template generator needs to be able to display yes/no values when faced with examples that state "should be one of: true, or false".

This issue is a blocker for the issue mentioned above

Definition of done

• Templates can be generated with the proper examples loaded.