Add nil checks for generated API client response bodies

[coderabbitai]

Description

Throughout the codebase, generated API client response fields (e.g., JSON200, JSON202, JSON201) are accessed directly without nil checks. These fields are only populated when the response body deserializes successfully. A response with the expected status code but an empty or malformed body will leave these fields nil, causing a nil pointer panic.

Context

This pattern was identified during review of PR #57 (specifically in internal/api/providers/resource.go around line 153 where createResp.JSON202.Id is accessed), but it appears to be a widespread pattern throughout the codebase.

Proposed Solution

Add nil checks before dereferencing any generated client response body fields, for example:

• Check if resp.JSON200 == nil before accessing resp.JSON200.Field
• Return a descriptive error when the response body is nil despite receiving the expected status code

Related

• PR: fix: batch resource apply and fix variable sync status code  #57
• Comment: fix: batch resource apply and fix variable sync status code  #57 (comment)
• Requested by: @zacharyblasczyk