Add windows support for interactive web terminals.

Description

In %11.3 support for interactive web terminals was added. However windows is not supported. In https://gitlab.com/gitlab-org/gitlab-ce/issues/25990#note_106621022 we are already getting some requests for this.

Proposal

No technical proposal yet, but this should work the same as bash and any other executor.

Links to related issues and merge requests / references

https://gitlab.com/gitlab-org/gitlab-ce/issues/25990#note_106621022