Create work items at group level

What does this MR do and why?

This MR enables creating work items at group level. Note that this only handles work item create part and does not handle fetching the created work item, though it can be seen as part of the graphql response.

There are several challenges with getting work items at group level

• Scoping IIDs to group vs project. This is being extracted into separate MR !112900 (merged)
• Handling references for work items(issues) at both group and project level. This is being extracted into a separate MR as well !113080 (merged)
• Handle any permission updates to allow creation of work items at group level.
• The work item creation itself that would include changes to the service and mutation code.

Related Issues

• re #392992 (closed)
• re #393246 (closed)

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