Upgrade Validator's OpenMRS API to latest 2.6.x

[Ruhanga]

The validator currently relies on an older version of OpenMRS Core (2.3.6). This limitation prevents certain conditional loaders that require higher core versions from functioning, resulting in relevant domains not loading.

This issue will be addressed by facilitating a safe upgrade to OpenMRS Core version 2.6.x or higher on the validator.

[Ruhanga]

Hi @alaboso, @CynthiaKamau, there's this item that would be excellent to include in version 2.8.0 for completeness sake. If you have the bandwidth, it's worth looking into. Else we can already have a minor release and include it later.