Extensions API: Add support for application/zip uploads to bypass GovCloud WAF blocking

## Description

The Extensions upload endpoint (`PUT /api/v1/deployments/extensions/{extension_id}`) is being blocked by WAF in some environments with a `403 Forbidden`. This occurs because the `multipart/form-data` header is flagged as a security risk.

The terraform provider is using the cloud sdk to interact with the API, see [here](https://github.com/elastic/terraform-provider-ec/blob/449ad52c1fa94fbeb6632d1599c3fe2716e1cd06/ec/ecresource/extensionresource/upload.go), so the ask is to update the upload logic to allow the upload to happen with `application/zip` if using `multipart/form-data` is not possible.