Allow full paths in REST requests

[paulomarg]

WHY are these changes introduced?

Currently, we can't handle requests like access scopes (/admin/oauth/access_scopes.json) or token access (/admin/api_permissions/current.json), because these resources use custom paths instead of the default /admin/api/{version}/....

This means we can't easily reach those endpoints unless the code uses the base HTTP client that the REST one is built upon, which makes things unnecessarily complicated.

WHAT is this pull request doing?

This PR solves that problem by allowing REST calls in the Admin API client to be made using a full path. Therefore, requests like

$client = $client = new Rest($this->domain, 'token');
$response = $client->get('/admin/oauth/access_scopes.json');

work just like any regular request would.

Type of change

• Patch: Bug (non-breaking change which fixes an issue)
• Minor: New feature (non-breaking change which adds functionality)
• Major: Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have added a changelog entry, prefixed by the type of change noted above
• I have added/updated tests for this change
• I have updated the documentation for public APIs from the library (if applicable)

[teddyhwang]

instead of assuming $path has a / with the getRequestPath helper, can we instead:

Suggested change

	if (strpos($path, "/admin") !== 0) {
	$path = "/admin/api/$apiVersion$path";
	if ($path[0] != '/') {
	$path = "/admin/api/$apiVersion/$path";

[paulomarg]

parent::getRequestPath is set up to always ensure the path has a / at position 0, which of course we could change here, but I wasn't too keen on using just the slash as a marker for a full path because I felt it would be too error prone.

My main concern was that folks would try things like /product.json, which I think should just be prefixed with the default.