Built-in nscd into the docker image (a better dns caching service)

[louislam]

Fix #3371
Fix #3123

[solracsf]

@louislam FYI: https://unix.stackexchange.com/questions/28553/how-to-read-the-local-dns-cache-contents#211396

dnsmasq would be a much better option: https://dev.to/mterrel/fixing-dns-timeouts-in-docker-with-a-dns-cache-2565

[emitosolini]

Hi, maybe you could add a flag to disable it in docker... I don't really find the use case in our environment since we run our own internal dns server with custom timeouts and some special zones with hosts that are checked trough uptimekuma.
Thanks.