Remove Helm2to3 capabilities

Proposal to Remove Helm2to3 capabilities as they're not part of the template anymore and Helm2 is long gone

The following discussion from !179 (merged) should be addressed:

• @Alexand started a discussion: (+4 comments)

  @partiaga could you review this hotfix?

helm2-3 currently breaks the pipeline due to deprecated params. But @hfyngvason and I have assessed in the linked discussion that it's safe to remove it as Helm2 is long gone and the migration helpers are not part of the template anymore.

By removing them we can also remove many jobs from our pipeline and the pipeline should be faster in general. Also we'll be publishing less images.

Implementation guide

• We should remove all usage of helm2. This means the related script and tests.
• We should base the docker file only from the helm-install-image with helm3, and not helm-2to3 anymore.
• We should remove docs related to it.

Follow-ups

• Open follow-up issue/MR on the helm-install-image repo:
  • Stop building helm2 and helm-2to3 on the helm-install-image repo and remove the documentation about it.