This commit fixes #5040, the harbor-db image will only contain empty
databases, and harbor ui container will use migrate tool to run initial
SQL scripts to do initialization.  This is helpful for the case to
configure Harbor against external DB or DBaaS like RDS for HA deployment
However, this change will results some confusion as there are two tables
to track schema versions have been using alembic for migration, for this
release we'll try to use alembic to mock a `migration` table during
upgrade so the migrator will be bypassed, in future we'll consider to
consolidate to the golang based migrator.
Another issue is that the UI and adminserver containers will access DB
after start up in different congurations, can't ensure the sequence, so
both of them will try to update the schema when started up.