### 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


"""
        Waits until the import process on the Galaxy server has completed or the timeout is reached.
        :param task_id: The id of the import task to wait for. This can be parsed out of the return
            value for GalaxyAPI.publish_collection.
        :param timeout: The timeout in seconds, 0 is no timeout.
        """
        state = 'waiting'
        data = None
        
        if 'v3' in self.available_api_versions:
            full_url = _urljoin(self.api_server, self.available_api_versions['v3'],
                                'imports/collections', task_id, '/')
        else:
            full_url = _urljoin(self.api_server, self.available_api_versions['v2'],
                                'collection-imports', task_id, '/')
        display.display("Waiting until Galaxy import task %s has completed" % full_url)
        start = time.time()
        wait = 2
        while timeout == 0 or (time.time() - start) < timeout:
            try:
                data = self._call_galaxy(full_url, method='GET', auth_required=True,
                                         error_context_msg='Error when getting import task results at %s' % full_url)
            except GalaxyError as e:
                if e.http_code != 404:
                    raise