Add default metadatas to EXRs from 3Delight

[vNicolini]

Summary

Add default metadatas to EXRs from 3Delight similarly to the ones already available in Arnold's render outputs.

What

Add metadatas related to the following:

• sampling & ray depth
• rendertime
• memory consumption
• filter & filter size
• core/thread count and CPU used
• camera's name used for the render
• camera's focal lenght, f/stop (if applicable), shutter, filmback/aperture & focal distance (if applicable)

Why

It's really handy to do r&d and profiling in regard to rendering in general, would also provide additionnal, useful information in turntables/slapcomps, etc ....

See EXRs attached that demonstrate current default EXR metadatas of Arnold compared to 3Delight's EXRs_exemples.zip

[gkocov]

Per the NSI specs embedding render stats data to the rendered image file is done using an int embedstatistics outputdriver attribute. Adding a bool/int embedstatistics custom output parameter in a Gaffer Outputs node correctly creates the corresponding NSI outputdriver attribute, but when checking the rendered EXR image metadata I couldn't find any render stats metadata being added. I even tried exporting the NSI scene file from Gaffer and then rendering it in the shell with renderdl -stats which should force adding the render stats metadata, but still without results. I don't think Gaffer is doing anything wrong here, so it might be best to check with the 3DL devs regards this.