Add Node version update process

[lognaturel]

Follow-up from v2024.3 retrospective. In that release, we upgraded node to 22 and I had some hesitation around when it should be done and by whom.

I considered explicitly saying that I do the upgrade similar to what Collect does but I don't think it's necessary until we decide to document more of the release process here.

While here I changed the heading syntax to use # because it allows deeper nesting and I think it's easier to read.

Targets master since it's docs only.

What has been done to verify that this works as intended?

Read it.

Why is this the best possible solution? Were any other approaches considered?

It provides the info succinctly.

How does this change affect users? Describe intentional changes to behavior and behavior that could have accidentally been affected by code changes. In other words, what are the regression risks?

No user-facing change, this just documents existing process.

Does this change require updates to documentation? If so, please file an issue here and include the link below.

This is the docs update.

Before submitting this PR, please make sure you have:

• branched off and targeted the next branch OR only changed documentation/infrastructure (master is stable and used in production)
• verified that any code or assets from external sources are properly credited in comments or that everything is internally sourced