[v2.9] Add "v26.1.x" option for "Docker Install URL" dropdown for RKE1

[chiukapoor]

Is your feature request related to a problem? Please describe. As part of https://github.com/rancher/rancher/issues/45439 we're adding support for Docker 26.1.x.

Describe the solution you'd like UI dropdowns that allow picking "Docker Install URL" (e.g. on Node Template details page - not sure where else it may be referenced) should additionally have a "v26.1 (Recommended)" choice that populates https://releases.rancher.com/install-docker/26.1.sh when selected.

Describe alternatives you've considered Note that the "Docker Install URL" is editable and doesn't limit users to only the available choices, so they can specify https://releases.rancher.com/install-docker/26.1.sh manually before this enhancement is done. Consequently, the existing option "v26.0.x (Recommended)" should be changed to "v26.0.x".

Additional Information

When a new version of the docker install is published, the UI will fetch that version and mark it as the default. Our role usually involves adding the previous version to the hard-coded list to serve as a cache.

See rancher/ui#5045 and rancher/ui#5136 for examples of how this has been previously handled.