Add the depstool binary

Currently, it only supports a "validate" command that validates that the tool can parse the WORKSPACE file.

PiperOrigin-RevId: 481650085
diff --git a/WORKSPACE.bazel b/WORKSPACE.bazel
index 620ac8a..aa887dd 100644
--- a/WORKSPACE.bazel
+++ b/WORKSPACE.bazel
@@ -46,7 +46,7 @@
 
 http_archive(
     name = "com_google_googleurl",
-    sha256 = "a1bc96169d34dcc1406ffb750deef3bc8718bd1f9069a2878838e1bd905de989",
+    sha256 = "a1bc96169d34dcc1406ffb750deef3bc8718bd1f9069a2878838e1bd905de989",  # Last updated 2022-04-04
     urls = ["https://storage.googleapis.com/quiche-envoy-integration/googleurl_9cdb1f4d1a365ebdbcbf179dadf7f8aa5ee802e7.tar.gz"],
 )
 
@@ -71,9 +71,9 @@
 # https://github.com/google/re2/tree/abseil
 http_archive(
     name = "com_googlesource_code_re2",
-    sha256 = "906d0df8ff48f8d3a00a808827f009a840190f404559f649cb8e4d7143255ef9",
+    sha256 = "906d0df8ff48f8d3a00a808827f009a840190f404559f649cb8e4d7143255ef9",  # Last updated 2022-04-08
     strip_prefix = "re2-a276a8c738735a0fe45a6ee590fe2df69bcf4502",
-    urls = ["https://github.com/google/re2/archive/a276a8c738735a0fe45a6ee590fe2df69bcf4502.zip"],  # 2022-04-08
+    urls = ["https://github.com/google/re2/archive/a276a8c738735a0fe45a6ee590fe2df69bcf4502.zip"],
 )
 
 # -------- Load and call dependencies of underlying libraries --------