PagesDomainSslRenewalWorker being throttled by LetsEncrypt rate limits

See https://letsencrypt.org/docs/rate-limits/.

https://sentry.gitlab.net/gitlab/gitlabcom/issues/1182616/

Acme::Client::Error::RateLimited: Error creating new order :: too many new orders recently: see https://letsencrypt.org/docs/rate-limits/
  acme/client/faraday_middleware.rb:51:in `raise_on_error!'
    raise error_class, error_message
  acme/client/faraday_middleware.rb:35:in `on_complete'
    raise_on_error!
  acme/client/faraday_middleware.rb:20:in `block in call'
    @app.call(env).on_complete { |response_env| on_complete(response_env) }
  faraday/response.rb:61:in `on_complete'
    yield(env)
  acme/client/faraday_middleware.rb:20:in `call'
    @app.call(env).on_complete { |response_env| on_complete(response_env) }
...
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Error creating new order :: too many new orders recently: see https://letsencrypt.org/docs/rate-limits/