fix: allow 'T' in timestamp values in COPY operations

[olavloite]

COPY operations used the TimestampUtils from the PG JDBC driver. This
class does not accept timestamp values that contain a 'T' as a separator
between the date and time value. Instead, we'll rely on our own
Timestamp parser that we already have in place for wire-protocol
conversion.

Fixes b/240602999

[codecov]

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@@                  Coverage Diff                  @@
##             postgresql-dialect     #319   +/-   ##
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