FIX: kubernetes executor caches job overwritten variables

What does this MR do?

executorkubernetes caches overwritten values for Namespace and ServiceAccount across job executions.

This MR ensures such values are not cached.

Why was this MR needed?

See #2583 (closed)

Are there points in the code the reviewer needs to double check?

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Tests
  • Added for this feature/bug
  • All builds are passing
• Branch has no merge conflicts with master (if you do - rebase it please)

What are the relevant issue numbers?

Closes #2583 (closed)