[Istio] Drop usage of prow build jobs

[videlov]

Description

We need to drop prow build jobs in Istio Github actions. Docs:
https://github.com/kyma-project/test-infra/blob/main/cmd/image-builder/README.md#quickstart-guide

See previous tasks done for PR builds (in Notes).

Motivation

Neighbours want to drop prow in favour of azure dev ops jobs.

Contact(s): @Sawthis

PRs

• cicd: build manager with image builder on main #1010
• cicd: Dockerfile adjustment #1011
• Remove Istio and APIGateway main and pull build jobs test-infra#11847
• add workflow for release build with image-builder #1012
• Remove istio release image build jobs test-infra#11868
• bug: move image build from steps to jobs #1018
• cicd: separate int gardener tests between regular and release PRs #1021
• Add pipeline workflow for the release branch #1025
• Fix wrong if in the workflow #1027
• change job for environment key in workflow #1029
• Remove redundant job and fix typo #1031
• Update cicd docs #1033

AC [Reviewer | PO]

• Istio images on main and release branch are built by neighbours provided GH Action

TODO

• Update docs after the end of the changes

Attachments

• 11711
• green run on PR to release

Follow-up Issues

• ...