Update default version to 20

[stebogit]

Node 20 is the current and LTS release

[reynoldsalec]

Ah yes, default versions...they have caused great woe in Lando v3, and they probably will be removed entirely in Lando v4.

If we update the default version to Node 20, anyone with an existing project using a type: node service with no version specified will be silently updated to Node v20. That could cause some issues for folks...you're probably seeing why we're going to get rid of this concept in Lando 4 :)

Open to an argument @stebogit of why this would still be desirable...we have pushed up the default version on some other services where we felt it wouldn't cause issues, although I will say there have quite often been unintended consequences even then.

[stebogit]

I'm not sure what you mean by removing the "concept" of a default version: you will always install some version of node (like for any runtime), the point is which one.
Now, if you made the version a required parameter, so that it is clear which one the user installs, in v4 will be a breaking change (no silent update) easily fixable just adding the required version.

The current default v14 is super out of date and having people still using it for a project - unless specifically required by some legacy project - is just silly. For the time being (not sure how far is a v4 release) the docs should probably warn the user that the default installed version is very outdated.