Nuke: unified clip loader

[jakubjezek001]

Description

At the moment Openpype Nuke is using two different loaders for loading image sequence and video files. This was causing trouble when the user wanted to use Inventory Asset Switch in case of switching from video file to image sequence. For that reason a Repair Inventory action has to be written, for repairing old video and sequence loaders. The New LoadClip plugin is now replacing Load Sequence and LoadMov. So in case a production is ongoing and those two loaders were used, user has to first repair those containers in inventory manager and then he can update to newer available version.

To be able to implement Retiming Loader feature the concept of containerId knob, shared across all loaded nodes, had to be introduced. In reality, this is solving the long lasted bug which was prevailing to update timewarp / retime nodes and those had to be previously removed manually. The used concept had been inspired by following idea shared by @davidlatwe avalon-core:issue:474.

Since there was more class methods which needed to be created for members treatment, and also those might come handy also in other loaders lately. This had been added to new abstract class child of avalon.api.Loader.

Also the improvement of Settings definitions for LoadClip had been introduced. Representations are now Added to those which are set by default in Class attributes instead of overiding them by Settings. It had to be treated in Avalon-core as the required feature was not available in the disocvery plugins function.

Solving: https://support.pype.club/a/tickets/763

Testing Notes

1. Make sure Avalon Core is set to the correct branch (belows are details)
2. Start Nuke in any of you previously worked nuke workfile where any old loaders were created (if not create some before you checkout to these PRs)
3. To test Repair action open Nuke-menu/OpenPype/Manager and select andy of loaded containers and RMB click and go to actions and chose the repair action (red with gears)
4. Notice those loaders had been updated to LoadClip namespace.
5. No test the loading abilities of new LoadClip loader by going to Load tool and chose either supported image seqeunce or video files. Those supported could be found here. In case you wish to use some of your unsupported extension/representation just go to Settings/Project setting/Nuke/Load/LoadClip and add them into Representaions
6. Load those sequences or videos into the scene and look into its OpenPypeData knob for more metadata details - see if they are correct.

Dependencies:

avalon-core: ynput/avalon-core#376

[mkolar]

Task linked: PYPE-1907 nuke : OpenPype switch asset not working

[jakubjezek001]

here are supported extensions/representations for the LoadClip

[jrsndl]

Works for me.