HttpTestTrait - Allow one to easily authenticate subrequests

[totten]

Overview

Update HttpTestTrait to make it is easier for E2E tests to send authenticated requests on behalf of different users/contacts.

Step towards #21249

Before

The test writer must determine a specific credential (e.g. username+password or api_key or JWT) and send it as part of the request.

After

The test writer may pass the option authx_user or authx_contact_id to Guzzle. This will be converted to a JWT so that the HTTP call includes authentication credentials. A few examples:

// Add JWT credentials to every Guzzle request.
$http = $this->createGuzzle([
  'authx_user' =>  $GLOBALS['_CV']['DEMO_USER'],
]);
$response = $http->get('route://civicrm/dashboard');

// Add JWT credentials to a single request.
$http = $this->createGuzzle();
$response = $http->get('route://civicrm/dashboard', [
  'authx_user' =>  $GLOBALS['_CV']['ADMIN_USER'],
]);

// Perform a stateful login via JWT.
$http = $this->createGuzzle(['cookies' => new CookieJar()]);
$response = $http->get('route://civicrm/authx/login', [
  'authx_contact_id' => 100,
]);

Full list of options:

• authx_ttl (int): Seconds of validity for JWT's
• authx_host (string): Only send tokens for the given host. (Default per CIVICRM_UF_BASEURL)
• authx_contact_id (int): The CiviCRM contact to authenticate with
• authx_user (string): The CMS user to authenticate with
• authx_flow (string): How to format the auth token. One of: 'param', 'xheader', 'header'.

[civibot]

(Standard links)

• If this is your first pull-request for CiviCRM, please browse CONTRIBUTING.md for information about the development and testing processes.
• If you are reviewing this pull-request, you may wish to consult the test sites and the Review Standards (long template, short template).

[eileenmcnaughton]

@seamuslee001 thoughts? This seems 'safe' to me in that it seems to be not otherwise invoked & adds test cover / ease of testing. Maybe that is high enough bar for this one.

[seamuslee001]

This seems fine to me merging