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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.


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            return "";
        }
        return super.getAutoIncrementClause();
    }
    @Override
    protected String getAutoIncrementClause(final String generationType, final Boolean defaultOnNull) {
        try {
            if (getDatabaseMajorVersion() < 10) {
                return "";
            }
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        }
        if (StringUtil.isEmpty(generationType)) {
            return super.getAutoIncrementClause();
        }
        String autoIncrementClause = "GENERATED %s AS IDENTITY"; 
        return String.format(autoIncrementClause, generationType);
    }
    @Override
    public boolean generateAutoIncrementStartWith(BigInteger startWith) {
        try {
            if (getDatabaseMajorVersion() < 10) {
                return false;
            }
        } catch (DatabaseException e) {
            return false;
        }
        return super.generateAutoIncrementStartWith(startWith);