Feat/migrate store in system apiexport

[OlegErshov]

On-behalf-of: SAP aleh.yarshou@sap.com

[BREAKING CHANGE] Store resource has been moved from core.platform-mesh.io to system.platform-mesh.io apiexport. This PR supports this migration

Authorization models hasn't been changed as it was decided to leave them in user workspaces so they can be changed.

Migration strategy for existing environments:
Store reconciliation will be fine when ApiBindings are fine with new changes. Unfortunately kcp will not allow to re-bound already bounded resources. It means that it's not possible to fix ApiBindings without removing old ones. Removing ApiBinding leads to the removal of the all bounded in it resources. As system apiexport affects 2 workspaces :root:orgs,:root:platform-mesh-system for environment update it's required to remove core.platform-mesh.io ApiBindings from them. It leads to the removal of all organizations, accounts, stores and other resources specified in core.platform-mesh.io ApiBinding.

To continue with actual migration this issue should be resolved #587
Migration steps:

1. Do a backup of OpenFGA, Keycloak and all resources in the system as it's described in this migration guide https://github.com/platform-mesh/helm-charts/blob/main/docs/migration-0.3/migration-guide.md
2. Remove core.platform-mesh.io apibinidng in :root:orgs. It will remove all stores, accounts, workspaces in root:orgs
3. Recreate all Accounts by UI
4. Restore OpenFGA data as it's described in the guide https://github.com/platform-mesh/helm-charts/blob/main/docs/migration-0.3/migration-guide.md`

[aaronschweig]

This is a breaking change for existing deployments, but the PR doesn't mention that. Could we add some context to the description and also some instructions regarding mitigation for existing deployments?

A few things worth documenting:

1. Existing Store / AuthorizationModel resources under core.platform-mesh.io will stop reconciling once this is rolled out.
2. The core.platform-mesh.io/fga-tuples finalizer on those resources could leave them stuck on delete if nothing cleans it up.
3. How would the migration strategy look like