### 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


assert mock_open.mock_calls[1][1 'https://ga.com/api/%s/collections/namespace/collection/' \
                                            'versions/?page=2' % api_version
    assert mock_open.mock_calls[2][1 'https://ga.com/api/%s/collections/namespace/collection/' \
                                            'versions/?page=3' % api_version
    if token_type:
        assert mock_open.mock_calls[0][2]['headers']['Authorization'] == '%s my token' % token_type
        assert mock_open.mock_calls[1][2]['headers']['Authorization'] == '%s my token' % token_type
        assert mock_open.mock_calls[2][2]['headers']['Authorization'] == '%s my token' % token_type
@pytest.mark.parametrize('responses', [
    [
        {
            'count': 2,
            'results': [{'name': '3.5.1', }, {'name': '3.5.2'}],
            'next_link': None,
            'next': None,
            'previous_link': None,
            'previous': None
        },
    ],
    [
        {
            'count': 2,
            'results': [{'name': '3.5.1'}],
            'next_link': '/api/v1/roles/432/versions/?page=2&page_size=50',
            'next': '/roles/432/versions/?page=2&page_size=50',
            'previous_link': None,
            'previous': None
        },
        {
            'count': 2,