endpoints for upcoming, current and all policies of a type

[deer-wmde]

adds routes

/v1/policies/{policy_type}/current
/v1/policies/{policy_type}/upcoming
/v1/policies/{policy_type}

---

Two observations:

1. api route order matters
this one works:

    $router->get('v1/policies/current', ['uses' => 'PoliciesController@getCurrentPolicies']);
    $router->get('v1/policies/{policy_type}', ['uses' => 'PoliciesController@getPoliciesByType']);

this one doesnt: v1/policies/{policy_type} swallows the later ones:

    $router->get('v1/policies/{policy_type}', ['uses' => 'PoliciesController@getPoliciesByType']);
    $router->get('v1/policies/current', ['uses' => 'PoliciesController@getCurrentPolicies']);

2. Explicit nulling of active_from
Due to our PolicyFactory implementation we need to set active_from to null if we want it to be not filled.
this works:

        Policy::factory()->create([
            'policy_type' => 'terms-of-use',
            'active_from' => null,
        ]);

this fills with 'active_from' => now()

        Policy::factory()->create([
            'policy_type' => 'terms-of-use',
        ]);

https://phabricator.wikimedia.org/T432714