Lower maxRowGroupByteSizeForCopy
As proposed by @lhoestq, this PR reduces the value of `maxRowGroupByteSizeForCopy` from 500_000_000 to 300_000_000, so that it is compatible with `maxArrowDataInMemory` (300_000_000).

This should fix the `UnexpectedApiError` that we have in some full viewer pages.

Fix #1795.
Lower maxRowGroupByteSizeForCopy: As proposed by @lhoestq, this PR reduces the value of `maxRowGroupByteSizeForCopy` from 500_000_000 to 300_000_000, so that it is compatible with `maxArrowDataInMemory` (300_000_000).

This should fix the `UnexpectedApiError` that we have in some full viewer pages.

Fix #1795.