Allow code and signature gen to use multiple endpoints

[josephjclark]

At the moment, the prompts for code gen and siggen allow a single endpoint to have an adaptor function generated.

We need to be able to support multiple endpoints, so that we can do something likeopenfn generate adaptor mailchimp --endpoinnts triggerListMemberEvents,getListMemberEvents, getMember

Hopefully this is as simple as adding a comma separated list to the prompt? But that needs testing, I don't know if it'll affect the quality of the generated code.

[josephjclark]

I suppose a related thing is: generation at the moment takes an instruction, which must be passed by the client. But I'd prefer the inputs to all codegen to be a list of endpoints and an openAPI spec. The actual instruction is an internal implementation detail of the generator function.