zap -> slog for logging

Closes #471 (closed).

zap kas:

{"level":"info","time":"2024-07-03T12:12:24.061+1000","msg":"Running KAS","kas":"gitlab-kas/v0.0.0/00000000"}

zap agent:

{"level":"info","time":"2024-07-03T12:12:31.176+1000","msg":"attempting to acquire leader lease ns/agent-3-lock...","agent_id":3}

slog kas:

{"time":"2024-07-03T12:06:58.952098+10:00","level":"INFO","msg":"Running KAS","kas":"gitlab-kas/v0.0.0/00000000"}

slog agent:

{"time":"2024-07-03T12:07:49.987626+10:00","level":"DEBUG","msg":"Connection done","mod_name":"agentk2kas_tunnel","agent_id":3}

Ignore the generated code commit.