feat: set output optional for presistent cache

[gaius-qi]

Description

This pull request includes several changes to the RegisterPersistentCachePeerRequest structure and its validation logic, as well as a version bump for the dragonfly-api package. The most important changes include making the output_path field optional and updating the validation logic accordingly.

Changes to RegisterPersistentCachePeerRequest structure:

• pkg/apis/scheduler/v2/scheduler.proto: Changed the output_path field to be optional and added validation rules to ignore empty strings.
• proto/scheduler.proto: Updated the output_path field to be optional.
• src/scheduler.v2.rs: Modified the output_path field to use Option type, making it optional.

Updates to validation logic:

• pkg/apis/scheduler/v2/scheduler.pb.validate.go: Added checks for Tag, Application, and OutputPath fields, ensuring they are validated properly. [1] [2]

Version bump for dragonfly-api package:

• Cargo.toml: Updated the version from 2.1.2 to 2.1.3.

Related Issue

Motivation and Context

[chlins]

lgtm