[Docs RFC] Update caggs docs with a few extra notes

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Thank you for clarifications, my feedback to help someone who fell in my confusion would be:
I think it would be a good idea to add a warning on the real-time section to indicate that the last bucket data wont be included in the refresh even if the option timescaledb.materialized_only is set to true unless we use null end_offset .
Also maybe we add a warning that switching materialized_only from true to false when having a null end_offset could partially "materlize" a chunk and we wouldnt have correct aggregation
Maybe we can consider having a materialized_only_watermark that would allow today's data to be refreshed when having timescaledb.materialized_only = true

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Community Slack thread: https://timescaledb.slack.com/archives/C4GT3N90X/p1671547709506999?thread_ts=1671525992.671069&cid=C4GT3N90X

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