This currently doesn't add any structure to the logs, changing just
the handler and output format. It does also add Sentry logging support.
The `log-format` configuration value now accepts values `none`, `text`,
and `json`.
The previous commit has eliminated any way to use `ServeHealth()`,
but kept it around to not introduce breaking changes. This one has
no such constraint.
This is done using reflection to avoid boilerplate and potential desync
of the two configuration interfaces. The `[[wildcards]]` section did
not fit well into the "splat every config key" paradigm, so it is
unmarshalled as a whole from a JSON payload in an environment variable.
This commit also splits up the `Config` type into small per-section
struct types and removes most references to the global `config` in
favor of passing pointers to sections around.
A new option, `-print-config-env-vars`, shows the names and types of
all of the available configuration knobs.
