feat(plugins): core read-only scripts and user plugin system

Introduce plugin/<id> installs (zip, HTTPS git, example, fork),
jerapah-plugin.json manifests with jerapah semver ranges, isolated
plugin dirs under data/plugins, and app version 0.1.0. Core scripts
are non-editable; get-current-time moves to examples/plugins.

Co-authored-by: Nasyarobby Putra <nasyarobby@gmail.com>

packages/server/workflows/default/test.yaml

@@ -1,6 +1,6 @@
 name: jsonata
 scripts:
-  - get-current-time.js
+  - plugin/get-current-time
   - script: jsonata.js
     config: 
       expression: '{"message": data.datetime & " " & data.processId}'