Update upgrade md for new unified config for sql string mapping to utf8view when we release datafusion 49.0.0 #16428
Description
Is your feature request related to a problem or challenge?
#16290 Has been merged, so we need to update the doc for next release.
New unified config for sql string mapping:
map_string_types_to_utf8view
Describe the solution you'd like
No response
Describe alternatives you've considered
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Additional context
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