Add method to add headers

[gogl92]

As a developer In some cases I need to add certain headers to my requests, simliar to the token.

Proposed methods:

Orion.setHeader('x-custom-header', 'header value');

Orion.setHeaders([
    'x-custom-header' => 'header value',
    'x-custom-header2' => 'header value2',
]);

[gogl92]

Closing discussion as it needs to be on the Orion typescript SDK