Define ADO pipeline standard

[dekiel]

https://github.tools.sap/kyma/test-infra/issues/415

Description

Issues defined for #375 describe changes required for refactoring and improving a submission pipelines. These tasks describe best practices we should use for all existing and future pipelines. To let the team use a common way working with ado pipelines all best practices defined and agreements made during work on #375 must be written down. A document must contain example implementation described rules.

Reasons

We need a written standard of working with ado pipelines to align a team and create a reference document.