Add Technical Contact role and permissions documentation

[MXClyde]

Summary

• New page documenting the Technical Contact role for Mendix on Kubernetes and Mendix on Azure applications: what permissions it grants, how it's assigned, who should hold it, and how to review/transfer it
• Adds a cross-reference from the Mendix on Kubernetes overview page (_index.md)
• Corrects an outdated Technical Contact section on the existing "Deploying a Mendix App to a Mendix on Kubernetes Cluster" page — removes a superseded "before/after December 12" distinction (every application now gets a Technical Contact from creation) and clarifies that only the current Technical Contact can transfer the role
• Removes a now-inaccurate note on the same page stating the Environment Purpose section is hidden when no Technical Contact is set — no longer possible, since every application has one from creation

Context

This documentation page is a dependency for a related Portunus UI change (Jira DES-7633) that will link to it from the Change Technical Contact modal. See Jira DES-7397.

Test plan

• Verify front matter renders correctly (title, description, weight, URL) on the new page
• Verify the new page appears under Mendix on Kubernetes deployment docs at the expected URL
• Verify the FAQ section renders as expected (bold Q, plain A, per existing doc conventions)
• Verify the new cross-reference links (from _index.md and from the corrected deploy page) resolve correctly
• Verify the corrected deploy-page sections read coherently in context
• Docs team review for tone/style consistency with neighboring pages

🤖 Generated with Claude Code

[MXClyde]

Closing to open a fresh PR with a clean description.