Previously, when the liquibase.url, .username, and .password
properties were used to configure a DataSource specifically for
Liquibase that DataSource would never be explicitly closed. As it is
created by DataSourceBuilder with no explicitly configured type it
will use whichever connection pool is available and, therefore, will
create and keep open the pool's minimum number of connections. This
is an unnecessary use of resources both in the application and in the
database.

This commit updates LiquibaseAutoConfiguration so that if it uses
DataSourceBuilder to create a DataSource then it will also close that
DataSource once the database has been migrated.

Closes gh-9218