Update GitHub link to point to main branch

[marytlf]

related to rancher/rancher#51277

The current version points the script user-cluster.sh to master branch and it should be to main branch.

[LucasSaintarbor]

@marytlf Thanks for the PR. Should this script URL be updated for the other versions of the docs (i.e. v2.9, v2.11, v2.12, Latest)? If so may you update the following files with this change?

• docs/how-to-guides/new-user-guides/manage-clusters/clean-cluster-nodes.md
• versioned_docs/version-2.12/how-to-guides/new-user-guides/manage-clusters/clean-cluster-nodes.md
• versioned_docs/version-2.11/how-to-guides/new-user-guides/manage-clusters/clean-cluster-nodes.md
• versioned_docs/version-2.10/how-to-guides/new-user-guides/manage-clusters/clean-cluster-nodes.md
• versioned_docs/version-2.9/how-to-guides/new-user-guides/manage-clusters/clean-cluster-nodes.md

[pmkovar]

Btw, you can just update docs/how-to-guides/new-user-guides/manage-clusters/clean-cluster-nodes.md and then run ./backport_docs.sh version-2.12 version-2.11 version-2.10 version-2.9 from the repo root to save time.

[marytlf]

Thank you @LucasSaintarbor @pmkovar I am waiting for the frameworks team confirm that this script needs backport and then I will update the other documents.