Add support for REDMINE_DB_SCHEMA_SEARCH_PATH to configure custom PostgreSQL schema

[tienipia]

Summary

• Introduced REDMINE_DB_SCHEMA_SEARCH_PATH environment variable to allow configuring a custom PostgreSQL schema.
• Default behavior remains unchanged (public schema).

Usage

Set the REDMINE_DB_SCHEMA_SEARCH_PATH environment variable to the desired schema:

environment:
  REDMINE_DB_SCHEMA_SEARCH_PATH: custom_schema