### 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


actual_versions = api.get_collection_versions('namespace', 'collection')
    assert actual_versions == [u'1.0.0', u'1.0.1', u'1.0.2', u'1.0.3', u'1.0.4', u'1.0.5']
    with open(cache_file) as fd:
        final_cache = json.loads(fd.read())
    cached_server = final_cache['ga.com:']
    cached_collection = cached_server['/api/v2/collections/namespace/collection/versions/']
    cached_versions = [r['version'] for r in cached_collection['results']]
    assert cached_versions == actual_versions
def test_world_writable_cache(cache_dir, monkeypatch):
    mock_warning = MagicMock()
    monkeypatch.setattr(Display, 'warning', mock_warning)
    cache_file = os.path.join(cache_dir, 'api.json')
    with open(cache_file, mode='w') as fd:
        fd.write('{"version": 2}')
        os.chmod(cache_file, 0o666)
    api = GalaxyAPI(None, "test", 'https://galaxy.ansible.com/', no_cache=False)
    assert api._cache is None
    with open(cache_file) as fd:
        actual_cache = fd.read()
    assert actual_cache == '{"version": 2}'
    assert stat.S_IMODE(os.stat(cache_file).st_mode) == 0o666
    assert mock_warning.call_count == 1
    assert mock_warning.call_args[0 \
        'Galaxy cache has world writable access (%s), ignoring it as a cache source.' % cache_file
def test_no_cache(cache_dir):
    cache_file = os.path.join(cache_dir, 'api.json')
    with open(cache_file, mode='w') as fd:
        fd.write('random')
    api = GalaxyAPI(None, "test", 'https://galaxy.ansible.com/')
    assert api._cache is None