Maya: don't add reference members as connections to the container set 📦

[antirotor]

Fix

This is modifying reference loader behavior so it doesn't add all reference content as a connection to the container set. Those connections make scene much bigger and slower to load (and with heavy rig to the point of unusability). For more details see #1854

⚠️ this is affecting every point in workflow where references are used

Testing

When loading references, you should see only reference node (*_RN) under AVALON_CONTAINERS/your_subset. To see AVALON_CONTAINERS in Maya, check Ignore 'hidden in Outliner' in Outliner options:

Close #1854

[mkolar]

I've tried checking as much as I could think of including some nested referencing and it seems to work quite well apart from one thing, and I'm not sure if it's related. With this PR, I can only get assets into look manager from selection, but get all assets doesn't work.

[antirotor]

I've tried checking as much as I could think of including some nested referencing and it seems to work quite well apart from one thing, and I'm not sure if it's related. With this PR, I can only get assets into look manager from selection, but get all assets doesn't work.

hmm, that happens to me too. It is probably related to the way how content of _CON sets is used to determine assets loaded in the scene and because now it is only that reference node, it is broken.