Clarify delimiter accepted in CLI arguments with multiple values in docs

Summary

• cli.md: fix description of picodata run -c
• config.md: clarify delimiter for instance.peer
• cli.md: clarify delimiter for picodata run --peer

---

• Close nothing
• Cherry-pick to: 24.6 / 24.5 / 24.4 / 24.3 / 24.2
• Staging:
  • https://docs.binary.picodata.io/picodata/dixitix_mention_comma_delimiter/reference/cli/#run_peer
  • https://docs.binary.picodata.io/picodata/dixitix_mention_comma_delimiter/reference/cli/#run_config_parameter
  • https://docs.binary.picodata.io/picodata/dixitix_mention_comma_delimiter/reference/config/#instance_peer
• See also picodata#1050 (closed)