Add Validator Upgrade Guide

[thomivy]

Summary of changes

Added a guide to upgrade validator per shady's request:

https://deploy-preview-3--tangle-docs.netlify.app/docs/node/validator/upgrade-node/

Reference issue to close (if applicable)

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Code Checklist

• [x] I have tested that prove my changes are working as intended
• [ na] I have added necessary documentation (if appropriate)

[netlify[bot]]

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[thomivy]

This build is having the same deploy issues as our other docs, can fix it by doing: