Housekeeping (#8)

* Rename the provider to dockerbuild.
* Add Makefile targets required by CI.
* Add per-language test targets compatible with CI.
* Fix broken example yaml.
* Add gitignore exclusions to fix SDK generation in CI.
* Fix lint errors.
* Vendor pulumi CLI via `tools.go` instead of `.pulumi`.
* Consolidate `go.mod`s into one file, with a minimal `go.mod` for the
Go SDK.
* Add codecov.

tools/tools.go

@@ -0,0 +1,9 @@
+//go:build tools
+// +build tools
+
+// See https://play-with-go.dev/tools-as-dependencies_go119_en/ for an explanation of this file.
+package tools
+
+import (
+	_ "github.com/pulumi/pulumi/pkg/v3/cmd/pulumi"
+)