User namespaces are not treated as obscure

[richard-cox]

Setup

• Rancher version:
• Rancher UI Extensions:
• Browser type & version:

Describe the bug

• some upstream resources are rancher mechanism specific and not meant to be viewed or changed outside of rancher operations
  • namespaces that represent projects
  • namespaces that represent clusters
  • namespaces that represent users
  • etc
• these are classed as obscure and should be by default hidden to the user
  • there's a user avatar --> preference to show them show dynamic namespaces
• currently the obscure namespace u- is not classed as obscure so is incorrectly shown
• obscure namespaces must also be system based of which the current ones aren't
  • might require backend changes, given the u- namespace doesn't have the system annotation
  • it might also be a weird artifact and should be user- instead: [BUG] New users are created with a generated names prefixed by m- instead of u- rancher#56214 (comment)

To Reproduce
big hard given other bugs in series (see additional context)

Result

Expected Result

Screenshots

Additional context
bonus - there's a bug where u- namespaces are m- : rancher/rancher#56214

Bugs in series

1. Project/Namespace should respect header filter #18693
2. [BUG] New users are created with a generated names prefixed by m- instead of u- rancher#56214 not related (i got confused between name and associated local cluster namespace)
3. User namespaces are not treated as obscure #18695
4. Resources in obscure namespaces are not filtered out from lists #18696