bump version to v2.6.2

[Full Changelog](https://github.com/ansible-network/network-engine/bl…

…ob/devel/CHANGELOG.rst)

- 2.6.1 release of the `config_manager` Ansible role.
- Available on [Ansible Galaxy](https://galaxy.ansible.com/ansible-network/config_manager/)

bump version to 2.6.0 (#6)

This change bumps the version to 2.6.0 for release