Update conference POS guide once we add IP zone limiter exception

[pavlenex]

Two things highlighted by @rockstardev

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1. Update when this is in Add exclusion for rate zone limiter when user is logged in btcpayserver#6414
2. Add minimum version for the guide to 2.0.3 since we have a lot of updates and fixes

[pavlenex]

For this one we should only do Add minimum version for the guide to 2.0.3 since we have a lot of updates and fixes and also make sure to mention that user should be logged in to avoid rate limiting issues since in btcpayserver/btcpayserver#6414 we removed the limit for logged in users.