This commit excludes OSS-specific links and content
added in https://github.com/scylladb/scylladb/pull/17624
to separate files and adds the include directive `.. scylladb_include_flag::`
to include these files in the doc source files.
Reason: Adding the link to the Open Source upgrade guide
(/upgrade/upgrade-opensource/upgrade-guide-from-5.4-to-6.0/enable-consistent-topology)
breaks the Enterprise documentation because the Enterprise docs don't
contain that upgrade guide. We must add separate files for OSS and
Enterprise to prevent failing the Enterprise build and breaking the
links.
Closesscylladb/scylladb#18372
c0e4f3e646