Install hangs indefinitely

The install script uses some heuristics to determine if it is run interactively or not. This setup is broken and has some false positives, i.e. it determines that it runs interactively while in fact it does not. As a result, the install script hangs indefinetely.

There also isn't a flag to force skip the interactive shell setup, so there is no known workaround atm. Existing env vars like `DEBIAN_FRONTEND=noninteractive` are not considered, either.

Some ways to break this are
- by breaking the `-t 0` check, such as if you run the script remotely, see [this](https://tldp.org/LDP/abs/html/intandnonint.html#II2TEST)
- by running the install script via kaniko during a docker build

Start by locating the install script and reading its interactive-shell detection, including the -t 0 check and environment handling. Reproduce the hang in a remote or kaniko Docker-build context, then verify that noninteractive installation can skip shell setup through an explicit flag or supported environment setting.

Written by the indexing model from the issue text.