Actions "Headers" section error with {{ $body.input?.xxx }}

### Version Information

Server Version: 2.38.1
CLI Version (for CLI related issue):

### Environment

OSS
### What is the current behaviour?

I'm experiencing an error when using {{ $body.input?.xxx }} in the "Headers" section of Hasura Actions.

### What is the expected behaviour?

{{ $body.input?.xxx }} should be evaluated and the result should be included in the request headers.

### How to reproduce the issue?

1. Goto Actions
2. New Action Or Modify
3. Try to use {{ $body.input?.xxx }} in the "Headers" section.
4. Goto API
5. Call API

### Screenshots or Screencast


### Please provide any traces or logs that could help here.

### Any possible solutions/workarounds you're aware of?

I was able to work around this issue by adding request_transform.request_headers.add_headers to the metadata.

setting showRequestHeaders to true in the frontend source code.
[Link](https://github.com/hasura/graphql-engine/blob/release/v2.38/frontend/libs/console/legacy-ce/src/lib/components/Common/ConfigureTransformation/RequestOptionsTransforms.tsx#L35)

### Keywords
1. OpenAPI
2. Headers
3. add_headers
6. showRequestHeaders

Start by reading frontend/libs/console/legacy-ce/src/lib/components/Common/ConfigureTransformation/RequestOptionsTransforms.tsx around showRequestHeaders and reproduce the issue through a Hasura Action with {{ $body.input?.xxx }} in Headers. Compare the generated request with the request_transform.request_headers.add_headers workaround; done means the expression is evaluated and its result is included in the request headers.

Written by the indexing model from the issue text.