fix: template parse error when pre prompt include {{}} (#462)

api/core/prompt/prompt_template.py

@@ -14,6 +14,7 @@ class JinjaPromptTemplate(PromptTemplate):
     def from_template(cls, template: str, **kwargs: Any) -> PromptTemplate:
         """Load a prompt template from a template."""
         env = Environment()
+        template = template.replace("{{}}", "{}")
         ast = env.parse(template)
         input_variables = meta.find_undeclared_variables(ast)