### 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


return self._available_api_versions
    def _call_galaxy(self, url, args=None, headers=None, method=None, auth_required=False, error_context_msg=None,
                     cache=False):
        url_info = urlparse(url)
        cache_id = get_cache_id(url)
        if cache and self._cache:
            server_cache = self._cache.setdefault(cache_id, {})
            iso_datetime_format = '%Y-%m-%dT%H:%M:%SZ'
            valid = False
            if url_info.path in server_cache:
                expires = datetime.datetime.strptime(server_cache[url_info.path]['expires'], iso_datetime_format)
                valid = datetime.datetime.utcnow() < expires
            if valid and not url_info.query:
                
                path_cache = server_cache[url_info.path]
                if path_cache.get('paginated'):
                    if '/v3/' in url_info.path:
                        res = {'links': {'next': None}}
                    else:
                        res = {'next': None}
                    
                    
                    res['results'] = []