Replace nvm with asdf

[ssbarnea]

This replaces the used of nvm with asdf, which is a newer, more generic, build tool management solution, one that can also be used to manage python versions and lots of other tools uses in the build chain.

One extra benefit that we get from this is that we will be used the same versions of nodejs on CI and for local testing, as the tools does control this via the .tools-versions config file.

As seen in the PR, from now on we will be using node 18 as default node version, as this the default node used by currently supported versions of vscode and also by extest.

We will also keep one job (test-node-lts) that will test with latest LTS version of node, as of today this is 20. The goes of this is to keep our codebase ready for future bumping of node, once vscode and extest will switch to it.

Please test this change locally, as this will validate that you have a working asdf installation. Running task test should work if you configure it correctly.