Chown files to a custom user after building (fix file ownership) (#250)

* Chown files to a custom user after building

* Better describe `chownFilesTo` input

As suggested by @webbertakken: https://github.com/game-ci/unity-builder/pull/250#discussion_r624575666

Co-authored-by: Webber Takken <webber@takken.io>

* Simplify chown step in `build.sh`

Co-authored-by: Webber Takken <webber@takken.io>

Co-authored-by: Webber Takken <webber@takken.io>

dist/steps/build.sh

@@ -143,6 +143,12 @@ if [[ "$BUILD_TARGET" == "StandaloneOSX" ]]; then
   chmod +x $ADD_PERMISSIONS_PATH
 fi
 
+
+if [[ -n "$CHOWN_FILES_TO" ]]; then
+  chown -R $CHOWN_FILES_TO $BUILD_PATH_FULL
+  chown -R $CHOWN_FILES_TO $UNITY_PROJECT_PATH
+fi
+
 #
 # Results
 #