Exception occurs when running to_gis() on a WN with leaks

[kbonney]

Summary
Attempting to run the to_gis() method on a WaterNetworkModel which contains leaks causes an Exception:

Exception has occurred: AttributeError       (note: full exception trace is shown but execution is paused at: _run_module_as_main)
'Junction' object has no attribute 'link_type'

Example

import wntr

wn = wntr.network.WaterNetworkModel("Net3.inp")
node = wn.get_node("101")
node.add_leak(wn, area=1, start_time=0, end_time=3600)
wn.to_gis()

Environment
Provide information on your computing environment.

• Operating system: Ubuntu 22
• Python version: 3.10
• WNTR version: Latest fetch from main branch.

Additional context
The Exception appears to be caused because the str magic method in ControlAction assumes that _target_obj is a link. However, when a leak is added to a node a control is added with a _target_obj that points to a node rather than a link.