feat: add shebang attribute on py_console_script_binary (#2867)

# Background
Use case: user is setting up the environment for a docker image, and
needs a bash executable from the py_console_script (e.g. to run `ray`
from command line without full bazel bootstrapping). User is responsible
of setting up the right paths (and hermeticity concerns). There's no
change in default behavior per this diff.

Previously, prior to Bazel mod, this was possible and simple through the
use of `rules_python_wheel_entry_points` ([per
here](https://github.com/bazel-contrib/rules_python/blob/9dfa3abba293488a9a1899832a340f7b44525cad/python/private/pypi/whl_library.bzl#L507))
but these are not reachable now via Bazel mod.

# Approach
Add a shebang attribute that allows users of the console binary to use
it like a binary executable.

This is similar to the functionality that came with wheel entry points
here:

https://github.com/bazel-contrib/rules_python/blob/9dfa3abba293488a9a1899832a340f7b44525cad/python/private/pypi/whl_library.bzl#L507

With this change, one can specify a shebang like:
```starlark
py_console_script_binary(
    name = "yamllint",
    pkg = "@pip//yamllint",
    shebang = "#!/usr/bin/env python3",
)
```

Summary:
- Update tests
- Add test for this functionality
- Leave default to without shebang so this is a non-breaking change
- Documentation (want to hear more about the general approach first, and
also want to hear whether this warrants specific docs, or can just leave
it to API docs)

---------

Co-authored-by: Ignas Anikevicius <240938+aignas@users.noreply.github.com>