### 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


"""Render GalaxyAPI as a native string representation."""
        return to_native(self.name)
    def __unicode__(self):
        
        """Render GalaxyAPI as a unicode/text string representation."""
        return to_text(self.name)
    def __repr__(self):
        
        """Render GalaxyAPI as an inspectable string representation."""
        return (
            '<{instance!s} "{name!s}" @ {url!s} with priority {priority!s}>'.
            format(
                instance=self, name=self.name,
                priority=self._priority, url=self.api_server,
            )
        )
    def __lt__(self, other_galaxy_api):
        
        """Return whether the instance priority is higher than other."""
        if not isinstance(other_galaxy_api, self.__class__):
            return NotImplemented
        return (
            self._priority > other_galaxy_api._priority or
            self.name < self.name
        )
    @property
    @g_connect(['v1', 'v2', 'v3'])
    def available_api_versions(self):