[Platform] Default DB version for creating universes should be the same version as Platform

This is admittedly a problem that bothers us in internal portal usage more than real customers (who tend not to have so many db versions)

When there's many db versions available to YW, the default db software version in Create Universe flow (first version in the list below) seems to be based on sort order. Instead we should default the DB version to the same as the current Platform version (in the case below, that is 2.7.2.0-b194)

@hsiaosu-yb @ymahajan