Add GitHub Workflow to automate release generation

[joanlopez]

In order to align this jslib with what was discussed (and consensuated) for k6-jslib-summary, and set up here, this pull request:
- Removes the build directory from control versioned files, in favor of automated releases
- Sets up a GH Workflow to automate releases from Git tags push.
- Updates the contribution guidelines accordingly.

UPDATE (08/01)

It adds a new GitHub Workflow aiming the (future) automation of releases, heavily inspired by https://github.com/grafana/k6-jslib-summary/blob/main/.github/workflows/release.yml, but using Webpack & NPM instead of Yarn to adjust it to the project needs.

I left some comments in form of open questions inline.

[oleiade]

As we're at it, I thought of renaming the webpack command to build, to align it with what I've observed in the ecosystem. It's a rather small change I believe, but it would also help "hide" that we rely on webpack which feels like an implementation detail.

What do you think?

[joanlopez]

As we're at it, I thought of renaming the webpack command to build, to align it with what I've observed in the ecosystem. It's a rather small change I believe, but it would also help "hide" that we rely on webpack which feels like an implementation detail.

What do you think?

I prepared that in the first pull request I prepared around this, but then I did care less because in this second approach the folder isn't being versioned at all. But yeah, it's a minor but fair change, that I can easily add in this pull request. Thanks!

[olegbespalov]

TBH, after a discussion in treads, I think that maybe removing the build directory for k6-jslib-aws isn't a good thing (or perhaps it is too early to decide).

Also, I feel that the idea of porting the changes to the jslib.k6.io isn't completely clear without a prototype (a PR to the jslib.k6.io) that could demonstrate the new flow.

How about putting this PR on pause? I'll sketch up the PR with the routine automation I mentioned in #89 (comment), and we can continue the discussion.

[joanlopez]

Hey @olegbespalov, @oleiade,

After our discussion, and as per what's commented in #89 (comment), I decided to update this pull request to just add the release workflow, so at least we can turn that step into a 1-click automation (it just requires creating the tag) and move on.

Wdyt?