docs(harbor): document admin credentials retrieval via TenantSecrets API #522

Problem

The Harbor application docs page at content/en/docs/next/applications/harbor.md lists only chart parameters and does not document how a tenant user retrieves the Harbor admin password.

Until now this gap was masked by a bug: cozystack/cozystack#2541 fixes a resourceNames mismatch in the Harbor ApplicationDefinition that prevented the {name}-credentials Secret from appearing in the TenantSecrets API. Once that PR lands, the standard cozystack discovery path (TenantSecret) will actually return the Harbor admin password — but no documentation tells the user that.

Proposed change

Extend content/en/docs/next/applications/_include/harbor.md (and matching versioned copies once 2541 ships) with a "Retrieving admin credentials" section explaining the TenantSecret retrieval workflow.

Pattern to follow: Bucket and RabbitMQ already expose tenant credentials via the same apps.cozystack.io/user-secret label and would have parallel guidance once it is added.