Patroni integration

[levkk]

Description

Use Patroni's HTTP API to determine:

• server role (primary vs. replica)
• host health (up/down)

Docs: https://patroni.readthedocs.io/en/latest/rest_api.html#health-check-endpoints

Related: #108

[vitabaks]

It will be useful:

• replica lag detection

  /replica?lag=100MB

  To send traffic only to replicas with a lag no higher than the specified value.

• custom tags support

  /replica?tag_key1=value1&tag_key2=value2

  For example, it allows to send read-only traffic only to the desired data center/region.