Add builder field

[amaschas]

This pull request adds support for specifying a target builder when starting a reload build and provides feedback if a fallback builder is used. The changes update both the protobuf definitions and the generated JavaScript code to handle the new builder and builder_fallback_message fields.

Protobuf schema changes:

• Added an optional builder field to the StartReloadBuildRequest message, allowing clients to specify which builder to use (e.g., to target the new Viam build service).
• Added an optional builder_fallback_message field to the StartReloadBuildResponse message, which is present if the requested builder was unavailable and the default builder was used instead.

Generated JavaScript (build_pb.js) updates:

• Updated StartReloadBuildRequest:
  • Included the new builder field in object serialization, deserialization, and binary wire format methods. Added getter, setter, clear, and presence-check methods for builder. [1] [2] [3] [4]
• Updated StartReloadBuildResponse:
  • Included the new builder_fallback_message field in object serialization, deserialization, and binary wire format methods. Added getter, setter, clear, and presence-check methods for builder_fallback_message. [1] [2] [3] [4]

[cecilyViam]

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