Add autoload and autoinstall GUC (#484)

Add two GUC settings: `duckdb_autoinstall_known_extensions` and
`duckdb_autoload_known_extensions`, which are direct proxy for DuckDB
[settings](https://duckdb.org/docs/configuration/overview.html)
`autoinstall_known_extensions` and `autoload_known_extensions`.

Mark both option enabled by default.

README.md

@@ -157,12 +157,7 @@ Querying data stored in Parquet, CSV, JSON, Iceberg and Delta format can be done
 	LIMIT 100;
 	```
 
-Note, for Azure, you will need to first install the Azure extension:
-```sql
-SELECT duckdb.install_extension('azure');
-```
-
-You may then store a secret using the `connection_string` parameter as such:
+Note, for Azure, you may store a secret using the `connection_string` parameter as such:
 ```sql
 INSERT INTO duckdb.secrets
 (type, connection_string)

include/pgduckdb/pgduckdb_guc.h

@@ -6,6 +6,8 @@ extern char *duckdb_maximum_memory;
 extern char *duckdb_disabled_filesystems;
 extern bool duckdb_enable_external_access;
 extern bool duckdb_allow_unsigned_extensions;
+extern bool duckdb_autoinstall_known_extensions;
+extern bool duckdb_autoload_known_extensions;
 extern int duckdb_max_threads_per_postgres_scan;
 extern char *duckdb_motherduck_postgres_database;
 extern int duckdb_motherduck_enabled;

src/pgduckdb.cpp

@@ -26,6 +26,8 @@ char *duckdb_maximum_memory = strdup("4GB");
 char *duckdb_disabled_filesystems = strdup("LocalFileSystem");
 bool duckdb_enable_external_access = true;
 bool duckdb_allow_unsigned_extensions = false;
+bool duckdb_autoinstall_known_extensions = true;
+bool duckdb_autoload_known_extensions = true;
 
 extern "C" {
 PG_MODULE_MAGIC;
@@ -131,6 +133,14 @@ DuckdbInitGUC(void) {
 	                     "Allow DuckDB to load extensions with invalid or missing signatures",
 	                     &duckdb_allow_unsigned_extensions, PGC_SUSET);
 
+	DefineCustomVariable("duckdb.autoinstall_known_extensions",
+	                     "Whether known extensions are allowed to be automatically installed when a DuckDB query depends on them",
+	                     &duckdb_autoinstall_known_extensions, PGC_SUSET);
+
+	DefineCustomVariable("duckdb.autoload_known_extensions",
+	                     "Whether known extensions are allowed to be automatically loaded when a DuckDB query depends on them",
+	                     &duckdb_autoload_known_extensions, PGC_SUSET);
+
 	DefineCustomVariable("duckdb.max_memory", "The maximum memory DuckDB can use (e.g., 1GB)", &duckdb_maximum_memory,
 	                     PGC_SUSET);
 	DefineCustomVariable("duckdb.memory_limit",

src/pgduckdb_duckdb.cpp

@@ -139,6 +139,8 @@ DuckDBManager::Initialize() {
 	config.replacement_scans.emplace_back(pgduckdb::PostgresReplacementScan);
 	SET_DUCKDB_OPTION(allow_unsigned_extensions);
 	SET_DUCKDB_OPTION(enable_external_access);
+	SET_DUCKDB_OPTION(autoinstall_known_extensions);
+	SET_DUCKDB_OPTION(autoload_known_extensions);
 
 	if (duckdb_maximum_memory != NULL) {
 		config.options.maximum_memory = duckdb::DBConfig::ParseMemoryLimit(duckdb_maximum_memory);