chore: add PyPI History to google-cloud-capacityplanner (#14690)

Fixes googleapis/librarian#2523

```
[PyPI History][1]

[1]: https://pypi.org/project/<package>/#history
```

The anchor pattern above needs to be in each CHANGELOG.md to identify
the top of a `CHANGELOG` file as per the code below:


https://github.com/googleapis/google-cloud-python/blob/692a39cc973c93c747a767c8b77d65d2c4c7be9b/.generator/cli.py#L766-L767

Author: parthea

packages/google-cloud-capacityplanner/CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+[PyPI History][1]
+
+[1]: https://pypi.org/project/google-cloud-capacityplanner/#history
+
 ## 0.1.0 (2025-09-24)