Improve plugin scan detection using mediatype

[munishchouhan]

In the current implementation #912

1. We are using the container image name from the request
2. If the image name contains "nextflow/plugin", then it is a plugin scan; otherwise container scan

In this issue, we will propose a better solution

1. We will check the mediatype of the container
2. If its related to plugin , then it is a plugin scan; otherwise container scan