.github,cmd/cigocacher: add flags --version --stats --cigocached-host

Add flags:

* --cigocached-host to support alternative host resolution in other
  environments, like the corp repo.
* --stats to reduce the amount of bash script we need.
* --version to support a caching tool/cigocacher script that will
  download from GitHub releases.

Updates tailscale/corp#10808

Change-Id: Ib2447bc5f79058669a70f2c49cef6aedd7afc049
Signed-off-by: Tom Proctor <tomhjp@users.noreply.github.com>

.github/actions/go-cache/action.yml

@@ -5,6 +5,9 @@ inputs:
   cigocached-url:
     description: URL of the cigocached server
     required: true
+  cigocached-host:
+    description: Host to dial for the cigocached server
+    required: true
   checkout-path:
     description: Path to cloned repository
     required: true
@@ -25,6 +28,7 @@ runs:
       shell: bash
       env:
         URL: ${{ inputs.cigocached-url }}
+        HOST: ${{ inputs.cigocached-host }}
         CACHE_DIR: ${{ inputs.cache-dir }}
       working-directory: ${{ inputs.checkout-path }}
       run: .github/actions/go-cache/action.sh