Fix some incorrect memory handling

While running TimescaleDB under valgrind I've found
two cases of incorrect memory handling.

Case 1: When creating timescaledb extension, during the insertion of
metadata there is some junk in memory that is not zeroed
before writing there.
Changes in metadata.c fix this.

Case 2: When executing GRANT smth ON ALL TABLES IN SCHEMA some_schema
and deconstructing this statement into granting to individual tables,
process of copying names of those tables is wrong.
Currently, you aren't copying the data itself, but an address to data
on a page in some buffer. There's a problem - when the page in this
buffer changes, copied address would lead to wrong data.
Changes in process_utility.c fix this by allocating memory and then
copying needed relname there.

Fixes #5311

(cherry picked from commit 0746517)

src/process_utility.c

@@ -1505,7 +1505,8 @@ process_relations_in_namespace(GrantStmt *stmt, Name schema_name, Oid namespaceI
 
 	while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
 	{
-		Name relname = &((Form_pg_class) GETSTRUCT(tuple))->relname;
+		Name relname = palloc(NAMEDATALEN);
+		namestrcpy(relname, NameStr(((Form_pg_class) GETSTRUCT(tuple))->relname));
 
 		/* these are being added for the first time into this list */
 		process_grant_add_by_name(stmt, false, schema_name, relname);

src/ts_catalog/metadata.c

@@ -141,7 +141,7 @@ ts_metadata_insert(const char *metadata_key, Datum metadata_value, Oid type,
 	bool isnull = false;
 	Catalog *catalog = ts_catalog_get();
 	Relation rel;
-	char key_data[NAMEDATALEN];
+	NameData key_data;
 
 	rel = table_open(catalog_get_table_id(catalog, METADATA), ShareRowExclusiveLock);
 
@@ -157,10 +157,10 @@ ts_metadata_insert(const char *metadata_key, Datum metadata_value, Oid type,
 
 	/* We have to copy the key here because heap_form_tuple will copy NAMEDATALEN
 	 * into the tuple instead of checking length. */
-	strlcpy(key_data, metadata_key, NAMEDATALEN);
+	namestrcpy(&key_data, metadata_key);
 
 	/* Insert into the catalog table for persistence */
-	values[AttrNumberGetAttrOffset(Anum_metadata_key)] = CStringGetDatum(key_data);
+	values[AttrNumberGetAttrOffset(Anum_metadata_key)] = NameGetDatum(&key_data);
 	values[AttrNumberGetAttrOffset(Anum_metadata_value)] =
 		convert_type_to_text(metadata_value, type);
 	values[AttrNumberGetAttrOffset(Anum_metadata_include_in_telemetry)] =