Create schema and samples for non-400 write request errors

[jstirnaman]

          Seperately, can we have 2 separate examples so the user can delineate:

• per-line rejection (with something writtten).
• not per-rejection. Nothing written. Error message is NOT partialWriteErrorWithRejectedPoints. e.g. namespace errors

Originally posted by @wiedld in #5169 (comment)

[jstirnaman]

From @wiedld

I checked the code. We return a 400 BadRequest ("invalid") for:
Invalid namespaces, when you have autocreate-namespaces enabled.
Last I heard, serverless had namespace autocreate on by default. Whereas dedicated had it off.
If off, then it's another error (I think permissions 403 -- but I would have to check. It's another code layer.).
Wrong encoding of the request header or body.
Other errors that they are less likely to hit.
{
code: "invalid"
message: "body content is not valid utf8: invalid utf-8 sequence of 1 bytes from index 1"
}