Remove "with-helm=true" support from Preview Environments

[meysholdt]

Is your feature request related to a problem? Please describe

In preparation to delete the Helm Chart (#9842), delete the with-helm annotation support from Werft Jobs. With that change, Helm can no longer be used in preview environments.

Describe the behaviour you'd like

Delete all code that implements the following flag:

gitpod/.werft/jobs/build/job-config.ts

Line 90 in dbc5805

const withHelm = "with-helm" in buildConfig && !mainBuild;

Additional context

We should also confirm with all product teams that nobody still depends on this feature.

[meysholdt]

We should also confirm with all product teams that nobody still depends on this feature.

Outreaches:

• WebApp
• IDE
• Self-Hosted

[meysholdt]

Mads: Confirm that "with-observability" works with the installer in core-dev or decide that we don't support that in core-dev.

[meysholdt]

with-payment should also work before we can remove with-helm:

• Make "with-payment" flag work on harvester preview envs #9855

[meysholdt]

related: #9858.