Add "packageStoragePublish" function

[mtojek]

Follow-up: elastic/elastic-package#728

The goal of this issue is to support package publishing to the new Package Storage v2. I suggest the following design:

Function name: packageStoragePublish
Input parameters:

• buildPackagesPath - path to the directory with .zip files
• map containing all required credentials, secrets, work dirs, etc.

Actions:

1. Identify packages not published to the Package Storage.
2. Sign unpublished packages using the Elastic signing pipeline.
3. Publish packages and signatures using publishing job

In general, we have already implemented all these steps here. We need to move it to this repository.

Dear Robots, I think we can handle this on our own and ask you later for review.

[v1v]

We are moving to GH actions so no need work on this now