Adding fields to add values in headers

Problem/Motivation

We need to make a request to an API with values to pass in Headers.

Steps to reproduce

Go to 'Structure' > Create an 'External entity' > 'Storage' > Enter API values

Proposed resolution

I suggest to replace the current 'Header name' field or add a new textarea field where we can enter our header values.

API changes

Add the values entered in this new field in the API request.

The values has to be entered like this template:

key1:value
key2:value