Linear: user configurable mapping from issue scale to time estimate

With the introduction of the AI planner it would be very helpful if the issue scale estimates configured in Linear could be mapped to some time estimate when imported into Morgen. This would then allow the AI planner to use this time estimates to create a better plan, instead of just assuming every tasks takes amount of time.

This needs to be configured in the Linear integration config as the mapping will vary from team to team.

The current workaround seems to be to manually add time estimates ([1h]) to issue descriptions. This works and I think it would be great if this could still be used to override the mapping, but it is cumbersome especially if you end up assigning the same time estimate for the same issue scale all the time.