neonvm-controller: Rework zap setup & disable sampling

[sharnoff]

By default, zap enables "log sampling" when not in development mode. Unsurprisingly, we're finding that neonvm-controller logs are being dropped in production as a result of this.

I couldn't find a clean way to disable sampling without entirely constructing the zap.Logger from scratch, so that's what I did.

Notable changes:

• neonvm-controller's --zap-* flags have been removed
• neonvm-controller now hard-codes the logger config we were using before -- info log level, stack traces on panic, and ISO8601 time

More context here: https://neondb.slack.com/archives/C03TN5G758R/p1716775758112349?thread_ts=1716765298.436929 See also: #475

[sharnoff]

This is actually not quite working as intended. See e.g. stacktrace is included on error in this PR here, but not included on main here.

Will merge after that's working as expected. Hopefully it's not too bad.

[sharnoff]

Fixed in 887dea7f6ba6d058f0696cabe748cbaefa248879 + validated via CI logs that it's working as expected.