Use `vshn-lbaas-exoscale` module

[simu]

Use vshn-lbaas-exoscale module, this changes the resource names of all LB-related Terraform resources, which makes this a breaking change.

Checklist

• [x] Keep pull requests small so they can be easily reviewed.
• [x] Categorize the PR by setting a good title and adding one of the labels: bug, enhancement, documentation, change, breaking, dependency as they show up in the changelog
• [x] Link this PR to related issues.
• [x] Update module ref to use tag once https://github.com/appuio/terraform-modules/pull/18 is merged.

[simu]

Latest force pushes: I removed the additional exposed features, to move them to their own PRs, so we get a nicer changelog.