### 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


cache_file = os.path.join(cache_dir, 'api.json')
    cache_file_contents = '{"version": 1, "test": "json"}'
    with open(cache_file, mode='w') as fd:
        fd.write(cache_file_contents)
        os.chmod(cache_file, 0o655)
    GalaxyAPI(None, "test", 'https://galaxy.ansible.com/', no_cache=False)
    assert os.path.isdir(cache_dir)
    with open(cache_file) as fd:
        actual_cache = fd.read()
    assert actual_cache == cache_file_contents
    assert stat.S_IMODE(os.stat(cache_file).st_mode) == 0o655
@pytest.mark.parametrize('content', [
    '',
    'value',
    '{"de" "finit" "ely" [\'invalid"]}',
    '[]',
    '{"version": 2, "test": "json"}',
    '{"version": 2, "key": "ÅÑŚÌβŁÈ"}',
])
def test_cache_invalid_cache_content(content, cache_dir):
    cache_file = os.path.join(cache_dir, 'api.json')
    with open(cache_file, mode='w') as fd:
        fd.write(content)
        os.chmod(cache_file, 0o664)
    GalaxyAPI(None, "test", 'https://galaxy.ansible.com/', no_cache=False)
    with open(cache_file) as fd:
        actual_cache = fd.read()
    assert actual_cache == '{"version": 1}'
    assert stat.S_IMODE(os.stat(cache_file).st_mode) == 0o664
def test_cache_complete_pagination(cache_dir, monkeypatch):