Detect object borders to add collider

How a game objetc's border could be detected in order to add a collider? The picture below is from my Unity's Scene and Game views. I added a trail renderer on an empty gameobject and moved it so the trail showed a simple shape:

As can be seen in the left scene side, the "selection outline" gizmo is perfectly drawn around the object, even when the trail cross itself. Id like to detect (or re-generate) those positions to configure an edgecollider2d. I found some explanation using shaders but it's too advanced for me.

I'd appreciate a lot if anyone could provide a guidance or code to help me. I'm also considering paying for this help if anyone is interested.

Thanks in advance.