Initial provider implementation (#18)

This brings over the initial buildx prototype from pulumi/pulumi-docker
and fixes various build and release issues.

tools/tools.go

@@ -5,5 +5,7 @@
 package tools
 
 import (
+	_ "github.com/golangci/golangci-lint/cmd/golangci-lint"
 	_ "github.com/pulumi/pulumi/pkg/v3/cmd/pulumi"
+	_ "github.com/pulumi/pulumi/sdk/go/pulumi-language-go/v3"
 )