Add victoriametrics support + possibility to define global labels for Prometheus metrics

[awmackowiak]

Example configuration of Prometheus metrics supported by VictoraMetrics:

PROMETHEUS_ENABLE: True
PROMETHEUS_GATEWAY_PORT: 9091
PROMETHEUS_GATEWAY_JOB: vaas
PROMETHEUS_GATEWAY_LABELS: dc=dc,test=test,somelabels=labes
VICTORIAMETRICS_SUPPORT: True

Snippet of pushed metrics:

PUT /api/v1/import/prometheus/metrics/job/vaas HTTP/1.1
Accept-Encoding: identity
Content-Length: 589
Host: localhost:9091
User-Agent: Python-urllib/3.9
Content-Type: text/plain; version=0.0.4; charset=utf-8
Connection: close

# HELP queue_time_from_order_to_execute_task queue_time_from_order_to_execute_task
# TYPE queue_time_from_order_to_execute_task summary
queue_time_from_order_to_execute_task_count{dc="dc",somelabels="labes",test="test"} 1.0
queue_time_from_order_to_execute_task_sum{dc="dc",somelabels="labes",test="test"} 1.868500839918852e-05
# HELP queue_time_from_order_to_execute_task_created queue_time_from_order_to_execute_task
# TYPE queue_time_from_order_to_execute_task_created gauge
queue_time_from_order_to_execute_task_created{dc="dc",somelabels="labes",test="test"} 1.694068332621746e+09