feat: add the prepare plugin hook

BREAKING CHANGE: Committing or creating files in the `publish` plugin hook is not supported anymore and now must be done in the `prepare` hook

Plugins with a `publish` hook that makes a commit or create a file that can be committed must use the `prepare` hook.

lib/definitions/plugins.js

@@ -36,6 +36,12 @@ module.exports = {
       error: 'ERELEASENOTESOUTPUT',
     },
   },
+  prepare: {
+    default: ['@semantic-release/npm'],
+    config: {
+      validator: conf => !conf || (isArray(conf) ? conf : [conf]).every(conf => validatePluginConfig(conf)),
+    },
+  },
   publish: {
     default: ['@semantic-release/npm', '@semantic-release/github'],
     config: {