[Feature] UploadCSV

[bh2smith]

1. Introducing data upload endpoint according to https://docs.dune.com/api-reference/tables/endpoint/upload
2. exposes base router _post method as a public method to the entire client SDK. This makes sense so not to hinder the user (inline comments added).
3. There was a recent breakage on the error messaging that was also fixed here.
4. We also introduce a couple of new types (one SuccessResponse that should have existed a while ago) related to the function parameters.