Udapte .proto files to their latest version

Description

REAPI and RWAPI are evolving, .proto files copies need to be kept in sync.

This update noteworthy changes include:

• From remote_execution.proto:
  • Support for symlinks in build output.
  • Operation cancellation clarification.
  • Documentation updates.
• From http.proto:
  • Documentation updates.

Changes proposed in this merge request:

• Sync. .proto files with their reference versions.
• Regenerate Python interfaces.