Add Hetzner API limit watch

[vzakaznikov]

We need to monitor Hetzner API call usage.

[vzakaznikov]

We can probably overwrite the request method (https://github.com/hetznercloud/hcloud-python/blob/main/hcloud/_client.py#L266) in our new custom HClient where we added the user agent (https://github.com/testflows/TestFlows-GitHub-Hetzner-Runners/blob/main/testflows/github/hetzner/runners/hclient.py).

[vzakaznikov]

The API limit can be retrieved from the response headers.

HTTP/2 200 
date: Wed, 09 Oct 2024 18:04:44 GMT
content-type: application/json
content-length: 203
vary: Accept-Encoding
ratelimit-limit: 3600
ratelimit-remaining: 3599
ratelimit-reset: 1728497085
...

[vzakaznikov]

For Hetzner API usage we need something similar to https://github.com/testflows/TestFlows-GitHub-Hetzner-Runners/blob/main/testflows/github/hetzner/runners/api_watch.py.