SERVER-83258 add python toolchain to bazel build

bazel/toolchains/python_toolchain.BUILD

@@ -0,0 +1,35 @@
+load("@bazel_tools//tools/python:toolchain.bzl", "py_runtime_pair")
+
+filegroup(
+    name = "files",
+    srcs = glob(["**/*"]),
+    visibility = ["//visibility:public"],
+)
+
+filegroup(
+    name = "interpreter",
+    srcs = ["{interpreter_path}"],
+    visibility = ["//visibility:public"],
+)
+
+py_runtime(
+    name = "py_runtime",
+    files = [":files"],
+    interpreter = ":interpreter",
+    python_version = "PY3",
+    visibility = ["//visibility:public"],
+)
+
+py_runtime_pair(
+    name = "py_runtime_pair",
+    py2_runtime = None,
+    py3_runtime = ":py_runtime",
+)
+
+toolchain(
+    name = "python_toolchain",
+    exec_compatible_with = [{constraints}],
+    target_compatible_with = [{constraints}],
+    toolchain = ":py_runtime_pair",
+    toolchain_type = "@bazel_tools//tools/python:toolchain_type",
+)