codegen: add streaming support for application/octet-stream contents

[hughsimpson]

Adding support for application/octet-stream content types, via streamBody/streamTextBody. Since the correct output code to produce depends upon the server provider, this also adds the flag openapiStreamingImplementation.

There are more interpreters that this could support, but I figured that the 4 I've added are probably the most common and it should be easy to add support for others down the line.

I'd originally intended to support only Array[Byte] schemas, but I don't think that restriction is actually necessary; given that the implementing service will need to provide the serdes to/from the bytestream independently of the endpoint generation, and the Schema generation already seems to work pretty well, I figure it's probably fine just to use Schema.binary[$theFormat] and support the same range of types as the json endpoints.

This pr also refactors the SBT plugin a bit, since we'd reached the limit of the number of params that could be sustained by the old code.

[hughsimpson]

Annoyingly it turns out that this syntax was only supported up to 11 elems for some reason (Why 11? 🤷). Took a while to find a refactor of the sbt plugin that would support aggregation of more setting keys, but I think the solution I've settled on here should be fine for arbitrary N settings.

[adamw]

11 is 22/2, which is the tuple limit in Scala ;). Honestly, no idea where this comes from :)

[hughsimpson]

I think there might be some issue here with the sbt changes... trying to figure it out...

EDIT: seem to have fixed the issue. Very loose and barely-understood explanation would be something like: I'd misunderstood the semantics of binding a config struct setting from many individual structs, and so put a Def.sequence where there shouldn't've been one. The practical effect was that it somehow messed up the evaluation time of the source generators and meant additional downstream munging was getting ignored (I like to emit an HList instead of a List for the endpoints definitions because reasons, so need source generator composition to work when using this plugin)

[adamw]

Thanks!