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## Environment
**Liquibase Version**: 4.3.4

**Liquibase Integration & Version**: CLI

**Database Vendor & Version**: PostgreSQL 12

**Operating System Type & Version**: Ubuntu 20.04

## Description
Hello,

I'm facing the same problem that's described in [this forum thread](https://forum.liquibase.org/t/access-postgis-from-different-schema/4708/3) (I did not reply in the forum because the number of links in a comment is restricted for new users). I'm using postgis as well but I guess it's the same for any extension that you would install on the public schema. The problem is that liquibase sets the search_path to only the default schema.

In the code, this is done in [DatabaseUtils#initializeDatabase](https://github.com/liquibase/liquibase/blob/master/liquibase-core/src/main/java/liquibase/database/core/DatabaseUtils.java#L36), which is called from [PostgresDatabase#rollback](https://github.com/liquibase/liquibase/blob/master/liquibase-core/src/main/java/liquibase/database/core/PostgresDatabase.java#L421) and the rollback function seems to be called for each changeset, after the preconditions are checked, in [ChangeSet#execute](https://github.com/liquibase/liquibase/blob/master/liquibase-core/src/main/java/liquibase/changelog/ChangeSet.java#L614).

I think that the problem was introduced with this commit: https://github.com/liquibase/liquibase/commit/feb2412. Before that, the search_path was not forced for each changeset, and there was no problem using an extension from the public schema without using prefixes.

I guess that there was a good reason to force the search_path, but I think that there should be an option to override the default behavior and to allow the user to set a custom search_path.

## Steps To Reproduce
With postgis:

* Add the postgis extension to the public schema: `CREATE EXTENSION postgis;`
* Run liquibase on another schema (`my_schema`) with the following changeset:

```
create table my_schema.test_table (
     a_box        Box2D
)
```

Liquibase will fail with the following error:

```
ERROR: type "box2d" does not exist
```

Thanks.


package liquibase.database.core;
import liquibase.Scope;
import liquibase.database.Database;
import liquibase.database.OfflineConnection;
import liquibase.exception.DatabaseException;
import liquibase.executor.ExecutorService;
import liquibase.statement.core.RawSqlStatement;
import liquibase.structure.core.Schema;
public class DatabaseUtils {
    /**
   * Executes RawSqlStatements particular to each database engine to set the default schema for the given Database
   *
   * @param defaultCatalogName Catalog name and schema name are similar concepts.
   *                           Used if defaultCatalogName is null.
   * @param defaultSchemaName  Catalog name and schema name are similar concepts.
   *                           Catalog is used with Oracle, DB2 and MySQL, and takes
   *                           precedence over the schema name.
   * @param database           Which Database object is affected by the initialization.
   * @throws DatabaseException
   */
  public static void initializeDatabase(String defaultCatalogName, String defaultSchemaName, Database database)
              throws DatabaseException {