Add findEntity to complement getEntity

[aiwilliams]

getEntity throws an error when the entity is not found. This may force the developer to code this pattern:

let entity: Entity;
try {
  entity = await jobState.getEntity(...);
} catch (err) {
  entity = null;
}

When the entity is expected to possibly be not found, it is more expressive and less code to write:

  const entity = await jobState.findEntity(...);

[austinkelleher]

Super agree. I was thinking the same thing when I used it.