Use liquibase to deploy schema changes in api server

[VithikaS]

Since we are supporting only Postgres database now, we can look at liquibase to deploy schema changes. It will help with better versioning of database changes, keeping it always in sync with the application.

All schema changes should be backported to changelog.yaml. When application starts, liquibase will apply all the changes in changelog file to database so we need checks that changeset is not executed if database object already exists. Alternative is to let it fail and mark the changeset as already executed.

[nscuro]

I started working on a PoC for this during my holidays, but for vanilla DT: https://github.com/nscuro/dependency-track/commits/liquibase-poc

I realized that many indexes are ineffective for some RDBMSes, and that index declaration is different across RDBMSes as well. So even when supporting multiple, there's not really a way around proper migration management. Schema generation from DataNucleus just doesn't cut it.