[Docs] Provide best practices for the safest way of upgrading Elasticsearch

[rwaight]

Describe the feature:
Last week we discussed our upgrade documentation and ways we can improve the upgrade experience; for larger deployments, the proper order becomes important.

While we provide this high level overview for upgrading Elasticsearch, we should also include best practices around the safest way to upgrade Elasticsearch. We should include the order in which nodes should be upgraded (for example: do we suggest ingest-only nodes first, master nodes last?), especially for larger deployments.

For overall Elastic Stack upgrades, I've opened elastic/stack-docs#537 for best practices to be included.

[elasticmachine]

Pinging @elastic/es-docs

[debadair]

Are there additional recommendations that should be made, or can this be closed now that #47279 is merged?

[rwaight]

Hi @debadair, I'm checking with the team and will let you know if any additional recommendations should be made, thanks!

[inqueue]

Are there additional recommendations that should be made, or can this be closed now that #47279 is merged?

What we have looks good. I think this can be closed.