Add override_content_disposition for OpRead

[Xuanwo]

• Add override_content_disposition for OpRead
• Implement override_content_disposition support in s3

[Xuanwo]

Hi, @baszalmstra, would you like to help implement this issue? This can fix #1726.

[baszalmstra]

Should I also implement other override flags? These are the ones supported by S3:

• response-content-type
• response-content-language
• response-expires
• response-cache-control
• response-content-disposition
• response-content-encoding

[Xuanwo]

Should I also implement other override flags? These are the ones supported by S3:

I prefer to add response-content-disposition first.

[baszalmstra]

See: #1742