feat: add success and fail notification plugins

- Allow `publish` plugins to return an `Object` with information related to the releases
- Add the `success` plugin hook, called when all `publish` are successful, receiving a list of release
- Add the `fail` plugin hook, called when an error happens at any point, receiving a list of errors
- Add detailed message for each error

test/fixtures/plugin-errors.js

@@ -0,0 +1,5 @@
+const AggregateError = require('aggregate-error');
+
+module.exports = () => {
+  throw new AggregateError([new Error('a'), new Error('b')]);
+};

test/fixtures/plugin-identity.js

@@ -0,0 +1 @@
+module.exports = (pluginConfig, options) => options;