API Defs Follow-up

AC

• Add condenser_api.is_known_transaction
• Add database_api.is_known_transaction
• Update since for transaction_status_api.find_transaction

mentioned in commit 6c685d28

marked the checklist item Add condenser_api.is_known_transaction as completed

marked the checklist item Add database_api.is_known_transaction as completed

marked the checklist item Update since for transaction_status_api.find_transaction as completed

mentioned in merge request !103 (merged)

mentioned in commit eb68ecd9

closed with merge request !103 (merged)