Add code-only push support for Object Storage archives

[Jaytee-fn]

The change adds push support for code-only functions by uploading locally built archives to Object Storage.

This PR extends 'fn push' so that when a function is marked 'code_only: true', the CLI uploads the corresponding local archive to Object Storage instead of using the traditional container image push flow.

PR includes-

• detect code-only functions in 'fn push'
• resolve Object Storage target from the active context
• locate the local archive using:
  • ..zip
• upload the archive to Object Storage
• surface archive/config/upload failures clearly
• preserve existing image-based push behaviour for non-code-only functions

Validation
Successful push

fn push
Code-only archive uploaded successfully as ..zip

Missing archive

If the archive does not exist, error will clearly say the built archive was not found.

Missing context config

If object_storage_bucket_name or namespace is not present in the active context, error will clearly say the code-only Object Storage target is not configured.

Upload failure

If bucket/namespace are invalid, the Object Storage upload error should be surfaced clearly.