Remove incorrect references to downtime on restart

[ravindk89]

Summary

When I first wrote these docs I made some assumptions around the consequences of a restart.

After discussion with engineering, these sections are largely incorrect or misleading.

MinIO restarts are very fast - a few seconds long at most even for large clusters. Operations are atomic and strictly consistent. And S3 SDKs typically retry transparently. This means applications should not be aware at all of a restart assuming the admin is following best practices - namely simultaneous restart of all nodes/processes, no rolling restarts

Goals

• [] Better describe how restarts effect ongoing operations
• [] Remove incorrect warnings around downtime
• [] Create checklist for upgrades to better frame the optimal setup

Build Instructions

Create a Python venv using 3.9 + and activate it

Run make stage

python -m venv venv
source venv bin activate
pip install -r requirements.txt
make stage