chore(codersdk): move all tailscale imports out of codersdk (#12735)

Currently, importing `codersdk` just to interact with the API requires
importing tailscale, which causes builds to fail unless manually using
our fork.

codersdk/workspacesdk/workspacesdk_test.go

@@ -0,0 +1,39 @@
+package workspacesdk_test
+
+import (
+	"net/url"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"tailscale.com/tailcfg"
+
+	"github.com/coder/coder/v2/codersdk/agentsdk"
+)
+
+func TestWorkspaceRewriteDERPMap(t *testing.T) {
+	t.Parallel()
+	// This test ensures that RewriteDERPMap mutates built-in DERPs with the
+	// client access URL.
+	dm := &tailcfg.DERPMap{
+		Regions: map[int]*tailcfg.DERPRegion{
+			1: {
+				EmbeddedRelay: true,
+				RegionID:      1,
+				Nodes: []*tailcfg.DERPNode{{
+					HostName: "bananas.org",
+					DERPPort: 1,
+				}},
+			},
+		},
+	}
+	parsed, err := url.Parse("https://coconuts.org:44558")
+	require.NoError(t, err)
+	client := agentsdk.New(parsed)
+	client.RewriteDERPMap(dm)
+	region := dm.Regions[1]
+	require.True(t, region.EmbeddedRelay)
+	require.Len(t, region.Nodes, 1)
+	node := region.Nodes[0]
+	require.Equal(t, "coconuts.org", node.HostName)
+	require.Equal(t, 44558, node.DERPPort)
+}