Update Siren Documentation

[mabdh]

• Add a glossary section to introduce all key terms.
• Update concept section to explain all keys terms in details.
• Update guide flow wth an example journey. Check buf guide for reference.
• Complete reference to other things should move to references. Check Buf for reference.
• Update guides to accommodate CLI and API using docusaurus tabs.
• Create a full CLI reference and move it to reference section.
• Create a full API reference and move it to reference section.
• Remove empty pages. Merge monitoring, deployment and troubleshooting in deployment guide only.