feat(database): support configurable SSL mode for PostgreSQL and MySQL

Add ssl_mode configuration option to allow users to customize SSL/TLS
policy for database connections instead of hardcoding sslmode=disable
for PostgreSQL and having no TLS support for MySQL.

Changes:
- database.Config, DatabaseConfig: add SSLMode field
- PostgreSQL DSN: replace hardcoded sslmode=disable with configurable
value
- MySQL DSN: append &tls=<SSLMode> parameter when SSLMode is set
- Full config pipeline: INI/env -> DatabaseConfig -> Config -> DSN ->
subprocess
- New env var BH_DB_SSL_MODE and ini key [database] ssl_mode
- Updated config example and documentation

internal/constant/constant.go

@@ -193,6 +193,7 @@ var (
 	RuntimeDBPath        string
 	RuntimeDBDSN         string
 	RuntimeDBTablePrefix string
+	RuntimeDBSSLMode     string
 )
 
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