Maya: Fix Redshift cryptomatte multipartEXR

[tokejepsen]

Changelog Description

When using Redshift and rendering multipart EXRs, the instances for cryptomatte AOVs are getting falsely marked as multipart EXR even though they are being forced to be separate files by Redshift.

Since we cannot query the AOVs multipart individually, we'll need a hardcoded rule.

Ideally I guess AOVs should be separate instances in the publishing process but that is too big of a scope atm.

Testing notes:

1. Configure Redshift render in Maya for multipart EXR and add Cryptomatte AOVs.
2. Publish and validate that only the main render instance has "multipartExr": true in the metadata json.

[LiborBatek]

All working well with multipart EXR and Cryptomatte aov...

Here is a scrngrab of JSON with that attrib turned FALSE

The job were finnished successfully and also published fine.

Im also enclosing the JSON for clarification.
renderLookdevMain_metadata.json.txt

[tokejepsen]

@LiborBatek could I get another test of this?

[BigRoy]

Wish this could've been 'simpler' and 'cleaner' - but the big comment does explain some of the reasoning behind it. I guess it does what it should.

Code changes make sense - didn't test it.

[LiborBatek]

I re did the testing and all working ok, DL job finnished without any errors, all renders been integrated as well and finally the JSON file contain the multipart: false flag too...

All goood. good to go IMHO!