Allow patroni to be setup as a standby cluster
Summary
When setting up a Geo secondary node, if you are using patroni, you want to setup it as a standby cluster.
In order to setup patroni that way there are a few instructions to follow: https://patroni.readthedocs.io/en/latest/replica_bootstrap.html?highlight=standby%20cluster#standby-cluster
Those instructions require extra params in the bootstrap section (and in dcs.yml when updating an already bootstrapped patroni).
Proposal
Add support for the standby_cluster
set of extra params in both patroni.yml
bootstrap section and dcs.yml
one.