go: re-do the entire thing

This is a mega-change, but attempting to split this up further is
probably not worth the effort.

Summary:

1. Bump up bazel, rules_go, and others.
2. Switch to new go target naming (bye bye go_default_library)
3. Move go deps to go.mod/go.sum, use make gazelle generate from that
4. Bump up Python deps a bit

And also whatever was required to actually get things to work - loads of
small useless changes.

Tested to work on NixOS and Ubuntu 20.04:

   $ bazel build //...
   $ bazel test //...

Change-Id: I8364bdaa1406b9ae4d0385a6b607f3e7989f98a9
Reviewed-on: https://gerrit.hackerspace.pl/c/hscloud/+/1583
Reviewed-by: q3k <q3k@hackerspace.pl>
diff --git a/third_party/py/BUILD b/third_party/py/BUILD
index eadbafd..efa4a96 100644
--- a/third_party/py/BUILD
+++ b/third_party/py/BUILD
@@ -1,4 +1,7 @@
 load("@rules_python//python:pip.bzl", "compile_pip_requirements")
+
 compile_pip_requirements(
     name = "requirements",
+    # Allow setuptools and friends to be pulled in as @pydeps_setuptools.
+    extra_args = ["--allow-unsafe"],
 )