Add a GFP VAE surrogate modeling task.

[RMichae1]

For a poli-related project I require the GFP data-set as provided by the Listgarten group, as well as the CBas VAE to treat the GFP optimization task as a black-box free-form optimization problem.

[RMichae1]

Not yet solved. Should also account for:

• [x] poli_elbo_objective as the evidence lower bound likelihood for experiments,
• [x] poli_fluorescence to use the CBas reference GP directly as surrogate function

Implementational additions required by @RMichae1

[RMichae1]

GP objective and ELBO objective have been implemented and are now part of cbas_gfp objective