switch to Chainguard's netcat image

Description

CG's netcat is multi-arch (amd64 and arm64) so we can remove nodeSelector

https://github.com/sigstore/helm-charts/blob/main/charts/trillian/values.yaml#L138

https://github.com/chainguard-images/images/tree/main/images/netcat

I'm not very deep into this area yet, but I'd be happy to collaborate on a PR with you. What do you think?

the nc image from Chainguard is lacking sh

we use sh, sleep and nc in initContainer

helm-charts/charts/trillian/templates/trillian-log-server/deployment.yaml

Line 43 in 55e320e

    
           command: ["sh", "-c", "until nc -z -w 10 {{ template "mysql.hostname" . }} {{ .Values.mysql.port }}; do echo waiting for {{ template "mysql.hostname" . }}; sleep 5; done;"]

so I think we need to open a PR to Chainguard's images repo first to add busybox https://github.com/chainguard-images/images/blob/main/images/netcat/configs/latest.apko.yaml