Build dist file in CI

[mattias-p]

We should build the dist file in CI and save it as an artifact attached to the CI job.

It has been noted that this would be useful:

• during release testing, and
• during PR review.

Open questions:

• When this should be triggered?
• How and when are these artifacts cleaned up?

Follow-up:

• Create issues/PRs to do this in the other repositories too.

[matsduf]

Since this concerns most repositories I suggest this issue is moved to zonemaster/zonemaster.

* When this should be triggered?

Every time a PR against develop branch passes CI testing

* How and when are these artifacts cleaned up?

This I find in the Github settings for this repository:

What artifacts that are referred to I do not know. The ones in the releases are retained longer.

[matsduf]

Building the zip file in Zonemaster-GUI should preferably be included.