Allow to inherit values from other fields

[codescape]

As a user I want to be able to inherit values from the parent issue to other fields of the newly created subtasks. For example a story with the custom user field Developer should be able to be inherited to assign the subtasks.

Possible solution would be something like this:

- new subtask using the value of the story's custom field Developer
  assignee: @inherit(customfield(Developer))
- new subtask using the assignee of the story for a custom field Developer
  customfield(Developer): @inherit(assignee)

This is a customer feature request:

• https://codescape.atlassian.net/browse/CASUP-101
• https://codescape.atlassian.net/browse/CASUP-128
• https://codescape.atlassian.net/browse/CASUP-145
• https://codescape.atlassian.net/browse/CASUP-155

Possible syntax alternatives:

syntax	example for standard field	example for custom field	+/- simplicity	+/- unintended usage
@inherit(fieldname)	@inherit(author)	@inherit(customfield(Developer))	(-)	(+)
@inherit:fieldname	@inherit:author	@inherit:customfield(Developer)	(-)	(+)
@fieldname	@author	@customfield(Developer)	(+)	(-)
${fieldname}	${author}	${customfield(Developer)}	(+)	(0)
@{fieldname}	@{author}	@{customfield(Developer)}	(+)	(0)

Tasks

• decide about syntax
• implement
• update documentation for syntax

[codescape]

Current existing customer requests are limited to pulling specific field values into the summary of the newly created subtasks. This would make implementing this feature easier if we limit it to summary and description first.

- Designer @inherit(customfield(Designer)) needs to create a mockup with priority @inherit(priority)

[codescape]

New customer requests ask for inheriting values from custom fields like "Designer" to the "assignee" field of the newly created subtask.

- new subtask
  assignee: @inherit(customfield(Designer))

An alternative syntax would be:

- create design elements for: @inherit:summary
  assignee: @inherit:customfield(Designer)
- implement backend for @inherit:summary
  assignee: @inherit:customfield(Developer)
- update burndown for @inherit:customfield(Story-Points) points