APIRule controller discovers default domain

[strekm]

Description

In component setup of Kyma there's global helm override representing default domain that can be used for setting up APIRule CR. In modular Kyma there's no such thing as global overrides and each module should discover configurations.
APIRule controller should discover default domain from Kyma default gateway. Atm Kyma default gateway is created by Istio module. So APIRule controller can assume that there's always "default" domain present and it can be retrieved from default Kyma gateway.
Default domain should be reconciled in standard reconcile loops (create, update, time based), which means that change should happen on existing APIRules.

ACs:

• APIRule controller discovers domain
• documentation
• global.domainName removed from APIRule controller

PR

• Discover default domain from gateway #515

Reasons

modularisation

DoD:

• provide documentation
  - [ ] release notes and What's New updates for Kyma customers
• provide unit tests
• test on production-like environment
  - [ ] verify resource limits
• followup issue
  - [ ] create release and bump in kyma
• PR reviewer will verify code coverage and evaluate if it is acceptable

Attachments

part of: #130

[strekm]

#515