add v3.0.0 upgrade notes and changelog

Signed-off-by: Bruno Vieira <[email protected]>

4.0-Upgrade.md

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+# Upgrading to chartmogul-node 3.0.0
+
+This new version replaces the existing pagination for the `.all()` endpoints that used a combination of `page` and `per_page` parameters, and instead uses a `cursor` based pagination. So to list (as an example) Plans you now can:
+
+```javascript
+const ChartMogul = require('chartmogul-node');
+const config = new ChartMogul.Config('apiKey');
+
+// Getting the first page
+plans = ChartMogul.Plan.all(config, { per_page: 10, cursor: 'cursor==' })
+
+// This will return an array of plans (if available), and a cursor + has_more fields
+{
+    "plans": [
+        {
+            "uuid": "some_uuid",
+            "data_source_uuid": "some_uuid",
+            "name": "Master Plan"
+        }
+    ],
+    "has_more": true,
+    "cursor": "MjAyMy0wNy0yOFQwODowOToyMi4xNTQyMDMwMDBaJjk0NDQ0Mg=="
+}
+
+if (plans.has_more) {
+  more_plans = ChartMogul.Plan.all(config, { per_page: 10, cursor: plans.cursor })
+}
+```
+
+If you have existing code that relies on the `page` parameter, those requests will throw an error now alerting you of their deprecation.

CHANGELOG.md

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+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog],
+and this project adheres to [Semantic Versioning].
+
+[Keep a Changelog]: https://keepachangelog.com/en/1.0.0/
+[Semantic Versioning]: https://semver.org/spec/v2.0.0.html
+
+## [3.0.0] - 2023-09-15
+
+### Added
+- Support for cursor based pagination to `.all()` endpoints.
+- Changelog and 3.0.0 upgrade instructions.