Add support for sending suffix to code-gecko
According to https://cloud.google.com/vertex-ai/docs/generative-ai/learn/models, code-gecko allows an optional suffix
parameter:
For code completion, suffix represents the end of a piece of meaningful programming code. The model attempts to fill in the code in between the prefix and suffix.
This should provide more context and help eliminate extraneous lines in the suggestions from the model.
Edited by Stan Hu