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/go.mod b/go.mod
new file mode 100644
index 0000000..fa311ec
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,20 @@
+module frc971.org/971-Robot-Code
+
+go 1.17
+
+require (
+	github.com/buildkite/go-buildkite v2.2.0+incompatible
+	github.com/golang/protobuf v1.5.2
+	github.com/google/flatbuffers v2.0.5+incompatible
+	google.golang.org/grpc v1.43.0
+)
+
+require (
+	github.com/cenkalti/backoff v2.2.1+incompatible // indirect
+	github.com/google/go-querystring v1.1.0 // indirect
+	golang.org/x/net v0.0.0-20200822124328-c89045814202 // indirect
+	golang.org/x/sys v0.0.0-20200323222414-85ca7c5b95cd // indirect
+	golang.org/x/text v0.3.0 // indirect
+	google.golang.org/genproto v0.0.0-20200526211855-cb27e3aa2013 // indirect
+	google.golang.org/protobuf v1.26.0 // indirect
+)