refactor!(toolchain): remove uname dep in the repository_rule stage (#2406)

Before this PR we would shell out to `uname` on UNIX systems to get the
`arch`
of the toolchain - on Windows we would not need to do it because there
used to
be only a single Windows platform. With this change we can correctly
support
the resolution of the python interpreter on various platforms and I have
also
added an env variable to customize the selection, so that users can use
`musl`
or a `freethreaded` interpreter if they wish.

As part of this change, I have restricted visibility of the config
settings
used in the toolchain alias repo so that we are creating fewer targets.
This is
a very good time to do this before `1.0.0`.

Fixes #2145
Work towards #2276
Work towards #2386
Work towards #1211 to unblock #2402
Work towards #1361

---------

Co-authored-by: Richard Levasseur <richardlev@gmail.com>

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index b77918f..46ebbc8 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -86,7 +86,7 @@
 _py_gazelle_deps()
 
 # This interpreter is used for various rules_python dev-time tools
-load("@python//3.11.9:defs.bzl", "interpreter")
+interpreter = "@python_3_11_9_host//:python"
 
 #####################
 # Install twine for our own runfiles wheel publishing.