Refactor build pipeline to use woodpeckerci/plugin-docker-buildx

This commit removes the platform field from the matrix and replaces the plugins/docker image with woodpeckerci/plugin-docker-buildx in the build pipeline. It also updates the settings for registry, repo, platforms, tag, and username.

.woodpecker.yml

@@ -1,7 +1,4 @@
 matrix:
-  platform:
-    - linux/amd64
-    - linux/arm64
   os:
     - alpine
     - slim
@@ -10,16 +7,14 @@ matrix:
     - 18
     - 20
 
-platform: ${platform}
-
 pipeline:
   build:
-    image: plugins/docker
+    image: woodpeckerci/plugin-docker-buildx
     settings:
       registry: techio.dev
       repo: techio.dev/${CI_REPO}
-      tags:
-        - ${version}-${os}
+      platforms: linux/amd64,linux/arm64/v8
+      tag: ${version}-${os}
       build_args:
         - tag=${version}-${os}
       username: deploy