gomemcached - mock generation to use mockery config file

gomemcached has used the old style of mockery generation. Now, the old style is being deprecated and a new one is to be used, with a YAML config file.

See: https://landontclipp.github.io/blog/2023/06/21/introducing-mockerys-new-packages-feature/
And
https://github.com/vektra/mockery/discussions/549

This MB is to update the goxdcr repo such that mock generation for unit test will use the new format.