Fix STACKIT documentation issues from review

[MXClyde]

Summary

This PR applies the review fixes for mendix/docs#11208 so they can be merged into the stackItdocumentation branch before that PR lands in development.

Casing standardization

• Standardize all "StackIt" / "Stackit" mentions to the official STACKIT all-caps spelling across the affected files.
• Rename "Stackit Postgres Flex" to "STACKIT PostgreSQL Flex" in the supported environments list.

Release note (mendix-for-private-cloud.md)

• Replace the one-line STACKIT release note with a complete entry that:
  • Lists the four newly supported STACKIT services (SKE, PostgreSQL Flex, Object Storage, Container Registry) with links.
  • Calls out that customers self-provision SKE / PostgreSQL Flex / Object Storage before deploying Mendix.
  • Documents the two known limitations (CREATEROLE missing on PostgreSQL Flex; missing CreateUser / CreatePolicy / CreateBucket APIs on Object Storage) and how to work around them.

Supported providers (private-cloud-supported-environments.md)

• Add description of the unmanaged provisioning model for SKE.
• Add a statement that any SKE-offered Kubernetes version inside the Supported Versions range is supported.

Storage plans (private-cloud-storage-plans.md)

• Remove the duplicate 3-bullet field list (Endpoint / Access Key / Type) under "Configuring the Plan" for STACKIT Object Storage; the longer field list immediately below already covers those fields.
• Fix grammar: fail to start the and deployment → fail to start, and the deployment.
• Fix grammar: By creating dedicated bucket for all the environment → By creating a dedicated bucket per environment.
• Fix double space: Enable this option and the bucket → Enable this option and the bucket.

Registry (private-cloud-registry.md)

• Revert the unrelated 4-space → 8-space reindent of the gcloud iam service-accounts add-iam-policy-binding block (lines 200-205) so the diff stays focused on STACKIT changes.
• Fix sentence: the registry created in stackit → the registry you created in STACKIT.
• Remove trailing whitespace from the STACKIT registry table.

License manager (private-cloud-license-manager.md)

• Revert the unrelated removal of the https<s>://pclm.<domain>/metrics health-check bullet — that endpoint still works and the deletion was outside the scope of the STACKIT PR.

Test plan

• CI lint passes on the updated branch
• Render the affected pages with Hugo and confirm:
  • Release note renders as a bulleted list with working links
  • Supported providers page shows the SKE provisioning note and version statement
  • Storage plans page shows a single field list under "Configuring the Plan" for STACKIT Object Storage
  • Registry page renders the gcloud snippet inside the numbered list (no broken indentation) and the STACKIT registry table has no trailing whitespace
  • License manager page shows both /health and /metrics bullets

[MXClyde]

Closing this PR as we've created a new PR against the main mendix/docs repository instead.

See the new PR: mendix#11290

It targets mendix/docs:development directly with all the same fixes, which is a cleaner path to landing the STACKIT documentation.