Rename CREATE_WORK_ITEM to CREATE_OR_UPDATE_WORK_ITEM

[edmorley]

Whilst reading the source to try and work out what gets synced and when, I saw the hook name CREATE_WORK_ITEM here:

git2gus/api/actions/createWorkItem.js

Line 118 in dbe8c53

name: 'CREATE_WORK_ITEM',

...which led to the impression that a work item would always be created whenever new labels were added. ie: If I swapped the labels around and switched from a bug to a user story, it seemed like Git2Gus would create a second work item rather than updating the original one.

However looking closer at the hook, I see it actually creates OR updates:

git2gus/api/hooks/issues-hook/index.js

Lines 20 to 21 in dbe8c53

	case 'CREATE_WORK_ITEM':
	return await createOrUpdateWorkItem(task);

Renaming CREATE_WORK_ITEM to CREATE_OR_UPDATE_WORK_ITEM would make this clearer :-)