### Summary

`ansible-galaxy collection install` makes a lot of requests to galaxy.ansible.com and can occasionally hit the rate limit. When that happens, galaxy.ansible.com will return a 520 http code and `ansible-galaxy` fails to download the collection and exits. Ideally when the client encounters a rate limiting http code (either 520, or 429), it should wait, slow down the request rate and try again rather than exiting.

More information is available here: https://github.com/ansible/galaxy/issues/2429 

### Issue Type

Bug Report

### Component Name

ansible-galaxy

### Ansible Version

```console
$ ansible --version
root@ubuntu-s-1vcpu-1gb-nyc3-01:~# ansible --version
ansible 2.10.7
  config file = None
  configured module search path = ['/root/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/local/lib/python3.8/dist-packages/ansible
  executable location = /usr/local/bin/ansible
  python version = 3.8.5 (default, Jan 27 2021, 15:41:15) [GCC 9.3.0]
```


### Configuration

```console
$ ansible-config dump --only-changed
root@ubuntu-s-1vcpu-1gb-nyc3-01:~# ansible-config dump --only-changed
root@ubuntu-s-1vcpu-1gb-nyc3-01:~#
```


### OS / Environment

All

### Steps to Reproduce

Run `ansible-galaxy collection install `amazon.aws`. If your internet is fast enough, this will occasionally fail when galaxy.ansible.com returns a 520 error code.

### Expected Results

Collection should be installed.

### Actual Results

```console
`ansible-galaxy` encounters a 429 or 520 http code and exits.
```


### Code of Conduct

I agree to follow the Ansible Code of Conduct


"""
        Fetch the list of related items for the given role.
        The url comes from the 'related' field of the role.
        """
        results = []
        try:
            url = _urljoin(self.api_server, self.available_api_versions['v1'], "roles", role_id, related,
                           "?page_size=50")
            data = self._call_galaxy(url)
            results = data['results']
            done = (data.get('next_link', None) is None)
            
            
            url_info = urlparse(self.api_server)
            base_url = "%s://%s/" % (url_info.scheme, url_info.netloc)
            while not done:
                url = _urljoin(base_url, data['next_link'])
                data = self._call_galaxy(url)
                results += data['results']
                done = (data.get('next_link', None) is None)
        except Exception as e:
            display.warning("Unable to retrieve role (id=%s) data (%s), but this is not fatal so we continue: %s"
                            % (role_id, related, to_text(e)))
        return results
    @g_connect(['v1'])
    def get_list(self, what):