chore: cleanup template building messages

[dobrac]

cleanup the template build messages:

• include the start command in the log message
• send only one log message when running the ready command
• change level to debug for the log message when the template is not ready
• do not print the exit status as it's already included in the error message. Let the downstream handle it itself
• log stderr as info level, not error (for a lot of tools, stderr is not an error)

---

Note

Streamline template build logs: include start command, consolidate ready message, downgrade non-ready logs to debug, align stderr log level, and avoid duplicate exit status; update tests accordingly.

• Orchestrator (template build):
  • Start: Log includes the command (builder.go), e.g., Running start command: <cmd>.
  • Ready:
    • Consolidate to a single info log: Waiting for template to be ready: <cmd> (ready.go).
    • Run ready command logs at DebugLevel and downgrade "not ready" messages to debug.
  • Command I/O:
    • Log stderr at the provided level (not forced to error) and avoid duplicate exit status output (sandboxtools/command.go).
• Tests:
  • Update expected logs to match new messages/levels in tests/integration/internal/tests/api/templates/build_template_test.go.

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