Make the deploy stamp the version and fire on Go changes

Two things in the deploy did not do what they looked like:

build-server passed --build-arg APP_VERSION, but the Dockerfile declares
ARG VERSION. An unknown build arg is ignored with a warning, so every
deployed image was stamped "dev": `keeporgd -version` and the image's
version label both said so, whatever the tag claimed.

The build pipeline's path filter listed 'VERSION', a file this repository
does not have, and '*.go', which under doublestar matches only top-level
Go files, of which there are none. So a push that changed only Go code or
only the version did not trigger a build. Now versions.mk and '**/*.go'.

Proved: built with --build-arg VERSION=0.5.0 and ran -version in the
container, which now reports 0.5.0.

.woodpecker/build.yaml

@@ -5,9 +5,9 @@ when:
         - 'config/variables/server.values.yaml'
         - '.woodpecker/build.yaml'
         - 'Makefile'
-        - 'VERSION'
+        - 'versions.mk'
         - 'Dockerfile'
-        - '*.go'
+        - '**/*.go'
     event: push
 labels:
   role: production