Support GATT database changes

[Vudentz]

Tests shall not assume handle positions are static on the database, if a handle is required for a test perform a lookup into the database to resolve the handle at runtime otherwise new aditions to the database can break the tests making EDTT inefective to be used in CI as it would likely generate false positives and block new features such EATT:

zephyrproject-rtos/zephyr#23199