Update documentation to adhere to latest API changes

What does this merge request do and why?

Updates documentation to use the updated API:

from

::Feature.enable(:index_code_with_zoekt)
::Feature.enable(:search_code_with_zoekt)
zoekt_shard = ::Zoekt::Shard.find_or_create_by!(index_base_url: 'http://127.0.0.1:6080/', search_base_url: 'http://127.0.0.1:6090/')
namespace = Namespace.find_by_full_path("flightjs") # Some namespace you want to enable
::Zoekt::IndexedNamespace.find_or_create_by!(shard: zoekt_shard, namespace: namespace.root_ancestor)

to

::Feature.enable(:index_code_with_zoekt)
::Feature.enable(:search_code_with_zoekt)
zoekt_shard = ::Search::Zoekt::Node.find_or_create_by!(index_base_url: 'http://127.0.0.1:6080/', search_base_url: 'http://127.0.0.1:6090/', uuid: '00000000-0000-0000-0000-000000000000')
namespace = Namespace.find_by_full_path("flightjs") # Some namespace you want to enable
::Zoekt::IndexedNamespace.find_or_create_by!(node: zoekt_shard, namespace: namespace.root_ancestor)

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.