title: Get related_name of Django ForeignKey field at runtime
body: <p>Let's say I have the following Django models:</p>
  
  <pre><code>class Person(models.Model):
      name = models.CharField(max_length=50)
  
  class Pet(models.Model):
      name = models.CharField(max_length=50)
      person = models.ForeignKey(Person, related_name='pets', on_delete=models.CASCADE)
  </code></pre>
  
  <p>I need to get the string value of <code>related_name</code> for <code>Pet.person</code> at runtime. I can get the <code>related_query_name</code>, which is <code>"pet"</code> but that's slightly different than the <code>related_name</code>, which is <code>"pets"</code>:</p>
  
  <pre><code>print(Pet._meta.get_field("person").related_query_name())
  # pet
  </code></pre>
  
  <p>Looks like the related name is on the <code>Person</code> class, but I'm not sure how to prove it's tied to <code>Pet.person</code>.</p>
  
  <pre><code>print("pets" in [f.name for f in Person._meta.get_fields()])
  # True
  </code></pre>
  
  <p>Is there anyway to do this?</p>