Outbound Requests don't automatically set the `Content-Length` header about spin

[lann]

https://www.rfc-editor.org/rfc/rfc9110#field.content-length

A server MAY send a Content-Length header field in a response to a HEAD request (Section 9.3.2); a server MUST NOT send Content-Length in such a response unless its field value equals the decimal number of octets that would have been sent in the content of a response if the same request had used the GET method.

A server MAY send a Content-Length header field in a 304 (Not Modified) response to a conditional GET request (Section 15.4.5); a server MUST NOT send Content-Length in such a response unless its field value equals the decimal number of octets that would have been sent in the content of a 200 (OK) response to the same request.

A server MUST NOT send a Content-Length header field in any response with a status code of 1xx (Informational) or 204 (No Content). A server MUST NOT send a Content-Length header field in any 2xx (Successful) response to a CONNECT request (Section 9.3.6).

But also, in agreement with this issue:

Aside from the cases defined above, in the absence of Transfer-Encoding, an origin server SHOULD send a Content-Length header field when the content size is known prior to sending the complete header section.

[karthik2804]

@vdice that is correct but as the SDKs do not live within Spin anymore, this issue is not relevant here(?)

[rylev]

One could imagine making this a tracking issue so that there is a central place that captures the issue for all SDKs instead of only independently tracking the issue across all SDKs.

[lann]

We should maybe only add it automatically when the known content length is non-zero; there are some cases when servers are supposed to not send it (notably 204 No Content).

[vdice]

Based on the results from #2249 it seems like the action items here would be to add this feature to various Spin SDKs, correct?