This commit removes the Enterprise upgrade guides from
the Open Source documentation. The Enterprise upgrade guides
should only be available in the Enterprise documentation,
with the source files stored in scylla-enterprise.git.
In addition, this commit:
- adds the links to the Enterprise user guides in the Enterprise
documentation at https://enterprise.docs.scylladb.com/
- adds the redirections for the removed pages to avoid
breaking any links.
This commit must be reverted in scylla-enterprise.git.
Closes#13298
73b74e8cac