Extend Provisioner to support the configuration of seeds within the same region as the shoot has

Description

As part of EPIC https://github.com/kyma-project/kyma/issues/18182, we are going to offer customers the option request a shoot and seed in the same region.

This requires a modification of the Provisioner logic to be able to

Receive the information that seed and shoot should be in the same region (will be an additional boolean flag)
Set the proper fields in the Shoot-spec for Gardener (label-selectors for seeds)

AC:

[ ] Provisioner contract gets extended to support also a boolean-field which indicates whether seed and shoot have to be in the same region
[ ] If this field is set, the Shoot-spec includes the required configuration (label-selectors for seed) to enforce that the shoot will only be created if a corresponding seed exists
[ ] Failure cases during the shoot provisioning (e.g. shoot hangs forever in Pending state) are detected and returned as failure to KEB.

Reasons

Enforce seed and shoot in same region to improve latency and address security related concerns.

Attachments

Relates to https://github.com/kyma-project/kyma/issues/18182

kyma-project / control-plane