WIP: patroni runbooks updates

This is a first iteration on improving procedures used for database related operations. For more context see: https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/7548

This MR should cover at least the following operations:

• add a new node, see if we have all the steps working correctly.
• in case of a minor failure, how can re-add a node.
• Remove a node from receiving traffic.
• Remove a node from the patroni possible failover.
• How to apply a change of a parameter in patroni/pgbouncer.
• how to restart/stop patroni.
• How to change of a parameter in pgbouncer.
• how to restart pgbouncer instance.
• How to connect to the PostgreSQL terminal or pgbouncer.
• how to execute a query on the variables of pgbouncer.
• How to perform a SQL statement in the Postgresql database.
• how to check-in Postgresql what queries are being executed on the moment ( pg_stat_activity view ) or during the last xxx seconds.
• mermaid graph with pgbouncer, patroni, postgres
• examples of EXPLAIN ANALYZE usage
• provide learning materials (e.g. links to Deep Dives, RCAs, exercises, books, course, etc)