Allow setting default credit for certain issue types

Problem/Motivation

For recurring events with many of the same people it would be nice to be able to have a default group.

For example on the podcast I have to manually add everyone.
While every week there are new guests, I have to always add myself, Stephen, John, and Martin.

Having defaults for recurring meetings or events would lower the barrier for crediting meetings and events.

Steps to reproduce

N/A

Proposed resolution

Add a way to add default credited users for a project and or issue type.

Remaining tasks

User interface changes

API changes

Data model changes