### 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


search_url = _urljoin(self.api_server, self.available_api_versions['v1'], "search", "roles", "?")
        if search:
            search_url += '&autocomplete=' + to_text(urlquote(to_bytes(search)))
        tags = kwargs.get('tags', None)
        platforms = kwargs.get('platforms', None)
        page_size = kwargs.get('page_size', None)
        author = kwargs.get('author', None)
        if tags and isinstance(tags, string_types):
            tags = tags.split(',')
            search_url += '&tags_autocomplete=' + '+'.join(tags)
        if platforms and isinstance(platforms, string_types):
            platforms = platforms.split(',')
            search_url += '&platforms_autocomplete=' + '+'.join(platforms)
        if page_size:
            search_url += '&page_size=%s' % page_size
        if author:
            search_url += '&username_autocomplete=%s' % author
        data = self._call_galaxy(search_url)
        return data
    @g_connect(['v1'])
    def add_secret(self, source, github_user, github_repo, secret):