Include reference to XC docs for namespaces during the "next" release

[mjang]

Based on https://github.com/nginx/documentation/pull/434/files

Description

Namespaces. Include this content with the N1C release notes, which correspond to the next XC release, scheduled for May 2025

Then you may lose access to those resources. To regain access, create the matching namespace in your F5 Distributed Cloud (F5XC) tenant, and assign necessary [RBAC](https://docs.cloud.f5.com/docs-v2/administration/how-tos/user-mgmt/roles) permissions to access that namespace.

Acceptance criteria

[weli02]

https://f5.slack.com/archives/C061UJ9HLKS/p1745854769609319

[mjang]

https://f5.slack.com/archives/C061UJ9HLKS/p1745854769609319

Note: this is a link to an internal discussion which confirms the content of this PR

[weli02]

Saving the content before I remove from my PR
If you already have set up resources in a namespace that:

• Does not exist in your F5 Distributed Cloud tenant
• Was deleted from your NGINX One Console tenant

Had a comment on this but otherwise looks good: https://github.com/nginx/documentation/pull/470/files#r2068648367

[mjang]

Complete:

• Changelog: Changelog update for Nginx One #481