When building with `CMake` (especially the targets `valkey-cli`,
`valkey-server` and `valkey-benchmark`) it is possible to have a
successful build while having warnings.
This PR fixes this - which is aligned with how the `Makefile` is working
today:
- Enable `-Wall` + `-Werror` for valkey targets
- Fixed warning in valkey-cli:jsonStringOutput method
Signed-off-by: Eran Ifrah <eifrah@amazon.com>
b3b4bdcda4