Add to configuration the option to disable `--function-context`

[antonakospanos]

--function-context adds a lot of boilerplate in the prompt for each line change reaching easily the limit of 5k token per commit.

We should provide the option developers disable it so that we support messages on longer commits too.

P.S. As a workaround developers can switch to GPT3 that supports 16k tokens too (model: gpt-3.5-turbo-16k)

Original reporter: @nikostoulas