Switch libcluster strategry from k8s to postgres

[IvanIvanoff]

Changes

Switch from using k8s labels to using postgres to connect the nodes in a cluster.
Also add the sanbase-admin to the cluster, so Metric Registry updates from the admin can be propagated to the

This will allow the clustering to also work locally. To run 2 instances locally that are connected in a node, you can use the following shell aliases:

alias imps='iex --cookie mycookie --name sanbase --erl "-kernel shell_history enabled" -S mix phx.server'
alias imps2='export PORT=4001 && iex --cookie mycookie --name sanbase2 --erl "-kernel shell_history enabled" -S mix phx.server'

Ticket

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have tried to find clearer solution before commenting hard-to-understand parts of code
• I have added tests that prove my fix is effective or that my feature works