Update CI with 3.0 release

[p7nov]

Details

We're releasing a new major Tarantool version – 3.0, and this adds a new doc version to the Tarantool website.
The doc build process needs to be updated accordingly.

What needs to be done

• The latest docs should be 3.0. This happens automatically when we merge the 3.0 doc branch to latest.
• A new workflow for publishing 2.11 docs is needed. We'll save them in the new branch named 2.11, and they should be published under the 2.11 LTS version on the site (see tarantool/tarantool.io#1488).

Definition of done

• A GitHub workflow for building 2.11 docs from the 2.11 branch is added.
• It publishes the docs under the 2.11 LTS version on the Tarantool website.
• All workflows with branches: 3.0 changed to branches: latest.