Too many historic pods causes querystring too long for Prometheus range_query API

[lujiajing1126]

Describe the bug

If we have many historic pods, the query expr will be very long. Then at some point, the request may be rejected by the gateway, e.g. Nginx. HTTP code 422 may be returned.

To Reproduce
Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior

Use POST API instead of GET.

https://github.com/4n4nd/prometheus-api-client-python/blob/39c5710521134fc450e9b4103cbb5995c05c5273/prometheus_api_client/prometheus_connect.py#L403-L409

But since we are using prometheus-api-client-python, it is not possible to do this.

Screenshots

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Smartphone (please complete the following information):

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Additional context
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[LeaveMyYard]

I have responded with a longer message in #67, but will repeat again here: we descided that using POST is a correct way and we can do that by subclassing the library connector