Downgraded Micrometer to 1.12.6

Micrometer has been downgraded to version 1.12.6.

In the previous AMP, Micrometer was upgraded to a new version (1.13.x) that is not fully supported by the current Spring Boot version (<=3.2). As a result, the Prometheus actuator did not work anymore. To fix that, the Micrometer version had to be downgraded.

(CMS-25076)