You can also do it in several steps, begin with a Dockerfile with instructions until before the interactive part. Then
docker build -t image1 .
Now just
docker run -it --name image2 image1 /bin/bash
you have a shell inside, you can do your interactive commands, then do something like
docker commit image2 myuser/myimage:2.1
The doc for docker commit
https://docs.docker.com/engine/reference/commandline/commit/
you may need to specify a new CMD or ENTRYPOINT, as stated in the doc
Commit a container with new CMD and EXPOSE instructions
For example some docker images using wine do it in several steps, install wine, then launch and configure the software launched in wine, then docker commit