Add repl_env dependency support

# 🚀 feature request

### Relevant Rules

Relevant rules are `//python/bin:repl` & `//python/bin:repl_env`.

### Description

Goal would be to enable repl use similar to how is is used now:
`bazel run @rules_python//python/bin:repl --@rules_python//python/bin:repl_dep=//python:my_rule_with_deps`
This is how I start interactive shells with access to runfiles and python packages depended on by the specified label.

It would be convenient to also enable the same for environment variables specified in that label. Could potentially be added to repl_dep. Alternative is:
--@rules_python//python/bin:repl_env=//python:my_rule_with_deps

### Potential Solution

Could add env attr assingment [here](https://github.com/bazel-contrib/rules_python/blob/bb2aad2d1e3f883c9cdc2264e0b4a2815233db57/python/bin/BUILD.bazel#L34).

kwargs forwarding should take care of any changes needed in py_binary_rule impl (I think).

Start at python/bin/BUILD.bazel around line 34 and inspect the //python/bin:repl and //python/bin:repl_env definitions, including how repl_dep is handled. Determine whether environment variables from the label passed to repl_dep should be supported or exposed through repl_env, then verify that the interactive shell receives those variables when run with the specified label.

Vom Indexierungsmodell aus dem Issue-Text verfasst.