fix(aws): populate default header for complete multipart request

[dentiny]

Rationale for this change

Hi team, when reading the code, I found CompleteMultipart doesn't populate the default headers

arrow-rs-object-store/src/aws/client.rs

Lines 787 to 792 in e89f62b

	let request = self
	.client
	.post(url)
	.query(&[("uploadId", upload_id)])
	.body(body)
	.with_aws_sigv4(credential.authorizer(), None);

While headers are added for other counterpart operations
PUT:

arrow-rs-object-store/src/aws/client.rs

Lines 541 to 544 in e89f62b

	let mut builder = self.client.request(Method::POST, url);
	if let Some(headers) = self.config.client_options.get_default_headers() {
	builder = builder.headers(headers.clone());
	}

GET:

arrow-rs-object-store/src/aws/client.rs

Lines 872 to 875 in e89f62b

	let mut builder = self.client.request(method, url);
	if let Some(headers) = self.config.client_options.get_default_headers() {
	builder = builder.headers(headers.clone());
	}

What changes are included in this PR?

This PR populate headers to complete multipart upload HTTP request.

Are there any user-facing changes?

No.

[crepererum]

thanks