Import gazelle

This patch imports gazelle as a linter. It automatically generates
BUILD file entries for Go code and at the same time keeps BUILD files
formatted.

The `tools/lint:run-ci` target is set up to automatically add new Go
repositories as well.

I added a tool at `//tools/go:mirror_go_repos` that needs to be run
before anyone can merge code that uses third-party Go libraries.

Change-Id: I1fbf6761439d45893f5be88d294ccc3c567840ca
Signed-off-by: Philipp Schrader <philipp.schrader@gmail.com>
diff --git a/tools/python/BUILD b/tools/python/BUILD
index 32093d3..9939653 100644
--- a/tools/python/BUILD
+++ b/tools/python/BUILD
@@ -18,11 +18,11 @@
 
 toolchain(
     name = "python_toolchain",
-    target_compatible_with = [
+    exec_compatible_with = [
         "@platforms//cpu:x86_64",
         "@platforms//os:linux",
     ],
-    exec_compatible_with = [
+    target_compatible_with = [
         "@platforms//cpu:x86_64",
         "@platforms//os:linux",
     ],