specify a postgres schema instead of depending on the default public?

[reecexlm]

When the anchor platform creates its database, it adds its tables to the “public” schema. We should expose a config option to allow developers to specify which schema to use for its tables.
Jira: ANCHOR-592

platform=# \d
List of relations
Schema | Name | Type | Owner
--------+-------------------------------------+----------+----------
public | custody_transaction | table | postgres
public | exchange_quote | table | postgres
public | flyway_schema_history | table | postgres
public | hibernate_sequence | sequence | postgres
public | sep24_transaction | table | postgres
public | sep31_transaction | table | postgres
public | sep6_transaction | table | postgres
public | stellar_payment_observer_page_token | table | postgres
public | stellar_payment_observing_account | table | postgres
public | transaction_pending_trust | table | postgres
(10 rows)