crosscluster/logical: rename user-created LWW column to avoid crdb_internal

[dt]

"crdb_internal" is supposed to be reserved for internal usage (it's right in the name), but a column that we'll ask users to create and interact with in a UDFs is not internal.

Release note: none. Epic: none.

[cockroach-teamcity]

This change is 

[dt]

TFTR!

bors r+

[craig[bot]]

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