Speed up CI and test in a matrix of Node 20–25

[janbrasna]

Description

The toolchain is already preinstalled on the runner, Jasmine is able to pick up all the browsers & drivers it's configured for. Removing the 1–2min of installation time, this enables expanding the runs to a matrix of Node versions (without wasting excessive resources), beyond what's used for publishing, to have some visibility and hints for consumers using different Node versions.

(With added caching the runs are changed to read-only.)

Also updates some prod docs deployment instructions.

• I have documented this change in the design system.
• I have recorded this change in CHANGELOG.md.

Issue

mozilla/bedrock#16872

Testing

https://github.com/janbrasna/protocol/actions/runs/21095848885 ✅

[janbrasna]

Hmmh git eventually decided there's too many changes along with the rename to track it as deletion and new addition instead of diffing the file:/ (I've renamed it from its GHA boilerplate defaults to actually match other uses to describe its content)… I see how this is not ideal, but I've made a diff on the side to hopefully make the changes more reviewable:

[janbrasna]

FYI this also upgrades actions version to Node 24 compatible ones to avoid run annotation warnings added to results. (ref mozilla/bedrock#17092)

[janbrasna]

There's a few things folded into this single PR to hopefully make it easier to ship the few changes in one go since it's pretty simple and short, however if it seems separating out the different bits (bumps, removal of preinstalled tools, rename, matrix strategy…) into distinct PRs would be beneficial I'm happy to split this up.

(Or if you want to see fresh CI runs since the logs have already expired, just lmk…)