feat: add is_preheat_request in DownloadTaskRequest

[SouthWest7]

Description

Added a flag is_preheat_request in DowanloadTaskRequest to indicate whether the task request is a preheat task.

Updates to

• proto/dfdaemon.proto: Update message DownloadTaskRequest adding a field is_preheat_request.

Related Issue

Motivation and Context

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation Update (if none of the other choices apply)

Checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.