[Feature Request] Allow negative indices to fixed_features in optimizers

[esantorella]

🚀 Feature Request

Allow negative indices to fixed_features and fixed_features_list in optimizers such as optimize_acqf

Motivation

This came up in #2602. It is tempting to describe the index of a feature with an index like "-1", but this is not currently supported.

Pitch

This should be easy to do by changing the indices to index % num_features.

Are you willing to open a pull request? (See CONTRIBUTING)

Only if users want this! Speak up if this would be useful for you (or would have spared your past self some hassle).