Add support for setting WandB Entity / Comet Workspace via experiment config

[IQisMySenpai]

This PR adds support for specifying the Weights & Biases (WandB) entity (team or organization) and the Comet workspace directly in the Nerfstudio experiment config.

Why?

Currently, users must either:

• Rely on their default WandB entity / Comet Workspace, or
• Move runs manually to the correct workspace after they have finished

This can be limiting when working across multiple teams or accounts. With this change, users can now explicitly set the WandB entity / Comet Workspace in the config through the workspace_name, making it easier to log runs under different teams or organizations without needing to modify global environment settings.

Notes

• The entity / workspace must already exist in WandB / Comet.
• If not specified, WandB / Comet will continue to fall back to the default entity (as it is currently), as defined in the user settings.

As this is my first PR to Nerfstudio, so I’m happy to take any suggestions or feedback!

[brentyi]

Is this argument useful for other writers, like Comet etc? If not, could we rename it to wandb_entity_name?

[IQisMySenpai]

It seems comet has something similar to entities called workspace, which is currently also defaulted to the user's workspace. I'll do some more research for the other writers and integrate their different entity solutions.

Should I also migrate to the new comet api or would you prefer this to be a separate PR?