Set 1.0.x release series as stable in the documentation

[julienrf]

Fixes #203

[tzach]

I do not see the change in https://migrator.docs.scylladb.com/stable/ yet.

[julienrf]

Indeed, the build failed: https://github.com/scylladb/scylla-migrator/actions/runs/10553978816/job/29235119336#step:5:125

I’ve asked @dgarcia360 for help.

[julienrf]

I think I found the cause of the issue: there is a requirement that branch names must start with branch-. I fixed our configuration accordingly and now the website shows both versions.