[API] Add case template API docs

[nadouani]

Add documentation of the following APIs:

• [x] Create case template
• [x] Update case template
• [x] List/Search case template
• [x] Delete case template
• [ ] Review

[nadouani]

@vdebergue the 403 response is stating Your are not authorized to create custom field, you haven't the permission manageCustomField. Is this true?

[vdebergue]

Fixed