### 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


with open(cache_file) as fd:
        actual_cache = fd.read()
    assert actual_cache == 'random'
def test_clear_cache_with_no_cache(cache_dir):
    cache_file = os.path.join(cache_dir, 'api.json')
    with open(cache_file, mode='w') as fd:
        fd.write('{"version": 1, "key": "value"}')
    GalaxyAPI(None, "test", 'https://galaxy.ansible.com/', clear_response_cache=True)
    assert not os.path.exists(cache_file)
def test_clear_cache(cache_dir):
    cache_file = os.path.join(cache_dir, 'api.json')
    with open(cache_file, mode='w') as fd:
        fd.write('{"version": 1, "key": "value"}')
    GalaxyAPI(None, "test", 'https://galaxy.ansible.com/', clear_response_cache=True, 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) == 0o600
@pytest.mark.parametrize(['url', 'expected'], [
    ('http://hostname/path', 'hostname:'),
    ('http://hostname:80/path', 'hostname:80'),
    ('https://testing.com:invalid', 'testing.com:'),
    ('https://testing.com:1234', 'testing.com:1234'),
    ('https://username:password@testing.com/path', 'testing.com:'),
    ('https://username:password@testing.com:443/path', 'testing.com:443'),
])
def test_cache_id(url, expected):
    actual = galaxy_api.get_cache_id(url)
    assert actual == expected