Generate: filter encoder inputs when its signature does not accept wildcards
# What does this PR do?

Now that we are moving towards any-to-text modalities, `generate` should be strengthened to work as-is without throwing exceptions just because a user has designed a slightly different architecture.

This PR enables the case where the model has some kwargs for operations between the encoder and the decoder -- i.e. for kwargs that can't be used in the encoder, but are also not decoder inputs. Normally, when a kwarg is not an encoder input, a `decoder_` prefix is added to its name, which is not the right argument naming in this case. Fortunately, the solution is simple :D 

This PR is a soft requirement to integrate [MM-CoT](https://github.com/amazon-science/mm-cot/tree/main), the alternative being the incorrect renaming of a few arguments to `decoder_(...)`.


_The documentation is not available anymore as the PR was closed or merged._<|||||>Tests for the feature added 👍 

The failing CI tests are two known failures, merging.