node-version output without `v`

Description:

I'd like to propose that we change the format of the outputs.node-version to not include v.

Justification:

The rational is that it's very easy to add the v with v${ steps.setup-node.outputs.node-version } but it's impossible to remove it since github does not give expressions to perform operations on strings.

The most mainstream usage i see of this (and i'm probably biased) is to pass the node-version installed in CI in a docker build with something such as ARG NODE_VERSION=22; FROM node:${NODE_VERSION}-alpine where obviously the v doesn't fit. Also semver computation would benefit from this as vX.Y.Z is not a semver compliant format.

Are you willing to submit a PR?

Yes, but I'd prefer directions before:

• Either it's made breaking and we keep node-version as a single output
• Either it's made non-breaking by introducing another parameter and adding a warning node to deprecate the 1st one - i have no idea how to name that parameter.

Start by tracing the outputs.node-version output contract and how the setup-node action currently formats it. Review existing output-related tests, then determine whether the change should be breaking or introduce a separate output; done means the selected contract is implemented, documented, and covered by tests.