Run containers as non-root

[flokli]

Containers now run as non-root, to improve compatibility with default PodSecurityPolicies in more recent versions of Kubernetes.

This is part of WPB-1234

Checklist

• Add a new entry in an appropriate subdirectory of changelog.d
• Read and follow the PR guidelines

[CLAassistant]

All committers have signed the CLA.

[jschaul]

@flokli nginz is failing to start:

Starting nginx
Setting up watches for /etc/wire/nginz/upstreams
nginx PID: 8
Setting up watches.
Watches established.
nginx: [alert] could not open error log file: open() "/var/log/nginx/error.log" failed (13: Permission denied)
2023/06/14 23:01:59 [warn] 9#9: the "user" directive makes sense only if the master process runs with super-user privileges, ignored in /etc/wire/nginz/conf/nginx.conf:1
2023/06/14 23:01:59 [emerg] 9#9: open() "/var/run/nginz.pid" failed (13: Permission denied)
/nix/store/b6v3ffbwxi028wdhhrxdmg4ywfj6yngs-reload-script/bin/.nginz_reload.sh-wrapped: line 12: kill: (8) - No such process
Stream closed EOF for test-n1/nginz-6754597db-mcf5d (nginz)

[flokli]

Seems the user directive may not be specified at all if nginx is already running as that user.