Document st2scheduler in HA #817
Description
The request is to document new st2scheduler for HA mode, how it works, what's needed and what to expect.
Similar to every other st2 component documentation, doc reference:
https://docs.stackstorm.com/reference/ha.html#components
If it's not implemented in full yet, still would be great to go with a doc describing future behavior at a high level.
Not to forget
Once the doc is ready, I'll need to update Helm Chart README here StackStorm/stackstorm-k8s#32 and respective Kubernetes service descriptions in https://docs.stackstorm.com/install/k8s_ha.html