Make manifest max_entries a user-configurable parameter

[arnold-support]

A couple of customers have hit the 100000 limit and got the "Cryptomatte: %lu entries in manifest, limiting to %lu" warning.

Could we make this a user parameter? We can add a warning to the documentation about the pros and cons of setting this limit higher.

[JenusL]

Yes this is a needed feature.

[ThiagoIze]

This is an easy fix (delete some code). Was there a reason for this limit @jonahfriedman ?