Support escape characters for {{moustache}} variables in the playground

[mmabrouk]

Description:
In the playground, we currently treat all {{double_bracket}} syntax as variables. However, some users have prompts where this syntax is used intentionally as part of the text—not as a placeholder. For example:

“In my original prompt I’m using double brackets to showcase some specific formats. I don’t want those to be considered as variables. Is there any escape character or anything similar I can use to override such behavior?”

Requested Feature:
Introduce a way to escape {{}} so that users can include them as literal text in their prompts without triggering variable substitution. This could be done with:
• An escape character (e.g. {{escaped}})
• A different syntax for literals
• A setting to disable variable parsing entirely

Use Case:
This allows users to write prompts with technical formats, documentation examples, or custom DSLs that happen to use {{}}, without needing workarounds.