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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.


protected SqlStatement getConnectionSchemaNameCallStatement() {
        return new RawCallStatement("select current_schema()");
    }
    /**
     * Generates PK following {@code PostgreSQL} conventions:
     * <li>Postgres PK size is limited with 63 bytes.
     * <li>Postgres PK is suffixed with '_pkey'.
     *
     * @param tableName Table name as the base name for the generated PK.
     * @return PK name.
     */
    @Override
    public String generatePrimaryKeyName(final String tableName) {
        final byte[] tableNameBytes = tableName.getBytes(CHARSET);
        final int pkNameBaseAllowedBytesCount = PGSQL_PK_BYTES_LIMIT - PGSQL_PK_SUFFIX.getBytes(CHARSET).length;
        if (tableNameBytes.length <= pkNameBaseAllowedBytesCount) {
            return tableName + PGSQL_PK_SUFFIX;
        }
        
        
        final String baseName = new String(tableNameBytes, 0, pkNameBaseAllowedBytesCount, CHARSET);
        return baseName.substring(0, baseName.length() - 1) + PGSQL_PK_SUFFIX;
    }
    @Override
    @SuppressWarnings("squid:S109")
    public int getMaxFractionalDigitsForTimestamp() {
        int major = 0;
        int minor = 0;
        try {
            major = getDatabaseMajorVersion();