[tcp]: Line Delimiter input text field does not work for control characters like \r about integrations

[elasticmachine]

Pinging @elastic/sec-deployment-and-devices (Team:Security-Deployment and Devices)

[taylor-swanson]

@andrewkroh, do you think this is an issue within Kibana/Fleet itself, or how we are building the agent file in the integration?

[andrewkroh]

I think we should try to make the UI work for this use case through collaboration with @elastic/fleet.

The other problem is properly building the YAML representation (you can use the API to set the line_delimiter to \n today, but it still won't work b/c the agent policy YAML is wrong). My preferred approach is to use {{{ to_json line_delimiter }}} where we depend on JSON serialization logic to properly write the string into the YAML file. This depends on removing these three lines that make the currently unused to_json handlebar function useless.