Header (SmallRye: GraphQL Client :: API 2.0.0.RC13 API)

```
@Retention(RUNTIME)
@Target({TYPE,METHOD,PARAMETER})
@Repeatable(Headers.class)
public @interface Header
```
Adds a custom header to the http requests sent out by the GraphQL Client. Annotate parameters, your method or the API interface.
The `name` is always fixed, but the value can be either a `constant` or the name of a `method` for dynamic values. It can't be both or neither. The method is always a static method, either on the interface itself (or one of the classes it's nested in) or any other class, when the method name is prefixed by the fully qualified class name plus . and is accessible, e.g. `java.lang.System.lineSeparator`.
In some cases, you may want to pass the value of a header as a parameter; neither `constant` nor `method` will be allowed then.
The `name` can be derived from the name of the parameter or method. It's mandatory for `constant` headers.
@Header annotations can be defined via @Stereotypes.

- Optional Element Summary
  
  Optional Elements
  Modifier and Type Optional Element Description
  
  String constant
  
  String method
  
  String name

- Element Detail
  - name
```
String name
```
    Default:
    
    ""
- - constant
```
String constant
```
    Default:
    
    ""
- - method
```
String method
```
    Default:
    
    ""