`doltgres version` prints inappropriate warning about being out of date and update instructions

[zachmu]

% doltgres version
dolt version 0.4.0
Warning: you are on an old version of Dolt. The newest version is 1.35.9.
To disable this warning, run 'dolt config --global --add versioncheck.disabled true'

Doltgres needs its own version command implementation.