- Require `letsencrypt/validator` package.
- Add a framework for registering configuration structs and any custom
validators for each Boulder component at `init()` time.
- Add a `validate` subcommand which allows you to pass a `-component`
name and `-config` file path.
- Expose validation via exported utility functions
`cmd.LookupConfigValidator()`, `cmd.ValidateJSONConfig()` and
`cmd.ValidateYAMLConfig()`.
- Add unit test which validates all registered component configuration
structs against test configuration files.
Part of #6052
Samantha