docs/releases.rst mentions non-existent maliput_rolling.repos

docs/releases.rst mentions maliput_rolling.repos multiple times. This file does not exist in https://github.com/maliput/maliput_infrastructure/tree/main/repos_index.

Ideally, releases.rst should be updated to document how Maliput automatically creaties releases and Bazel Central Registry pull requests based on tags.

Start with docs/releases.rst and verify the referenced maliput_rolling.repos path against the maliput_infrastructure repos_index. Document how Maliput creates releases and Bazel Central Registry pull requests from tags, and remove or correct the nonexistent-file references so the release documentation matches the current process.

Written by the indexing model from the issue text.