[API-Gateway] Drop usage of prow build jobs

[videlov]

Description

We need to drop prow build jobs in API-Gateway 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

ToDo [Developer]

• Fix scheduled api-gateway integration tests
• Introduce image-builder in release workflows
• Create test release 0.0 and clean it up afterwards
• Cherry pick workflow to release 2.6
• Purge test infra
• Update CI/CD docs

PRs

• Fix main integration test on schedule #1319
• Run integration tests in schedule without build #1323
• release pull request pipeline #1321
• Add image-builder to create release workflow #1324
• Cherry-pick release branch related workflows #1331
• remove remaining api gateway prow jobs test-infra#12016
• Update CI/CD documentation with new build job #1333

AC [Reviewer | PO]

• API Gateway images on main and release branch are built by neighbours provided GH Action
• Fix main workflow on schedule

DoD [Developer & Reviewer]

• Provide documentation.

Attachments

• Remove Release jobs from Prow
• Release PR workflow run
• Create release workflow run
• Release 2.6 PR workflow run
• Scheduled main integration run

[strekm]

revert main workflow cause scheduled int tests are failing