msgraph_resource_action overwrites custom Content-Type with application/json when body is set

When using msgraph_resource_action to call Microsoft Graph endpoints that require a non-JSON request body, custom Content-Type headers are ignored/overwritten.
Example use case: uploading Entra ID organizational branding image assets:
resource "msgraph_resource_action" "organizational_branding_assets" {
resource_url = "organization/${var.tenant_id}/branding/localizations/0/bannerLogo"
api_version = "v1.0"
method = "PUT"

headers = {
"Content-Type" = "image/png"
}

body = filebase64("${path.module}/branding/banner.png")
}
Expected behavior
The request should be sent with:
Content-Type: image/png
or the provider should provide a supported way to send raw/binary request bodies with a custom content type.
Actual behavior
Microsoft Graph receives:
Content-Type: application/json
and rejects the request:
Invalid Image Content-Type 'application/json'.
Root cause
In internal/clients/msgraph_client.go, MSGraphClient.Action applies custom headers first:
for key, value := range options.Headers {
req.Raw().Header.Set(key, value)
}
but then, when body != nil, it calls:
runtime.MarshalAsJSON(req, body)
req.Raw().Header.Set("Content-Type", "application/json")
This overwrites any user-provided Content-Type.
Impact
This makes msgraph_resource_action unusable for Microsoft Graph endpoints that require raw binary or non-JSON bodies, such as:
PUT /organization/{tenantId}/branding/localizations/{locale}/{streamProperty}
where Graph expects image/png, image/jpeg, etc.
Suggested fix
Either:
Do not overwrite Content-Type if the user already provided one in headers, or
Add support for raw body uploads, for example raw_body, body_base64, or similar, that bypasses JSON marshaling and respects the provided Content-Type.
Provider version
microsoft/msgraph v0.3.0

Start in internal/clients/msgraph_client.go at MSGraphClient.Action and trace how options.Headers and the request body are applied. Verify the behavior for a non-JSON body such as the branding image example; done means a caller-provided Content-Type is respected and Microsoft Graph receives the requested media type instead of application/json.