Add a DisplayNameKey struct to pass display names from routes through the task
parent hierarchy to the health monitor. This allows the health monitor to use
more descriptive names for logging instead of internal task names.
BREAKING CHANGE: The monitor.DisplayNameKey struct is now part of the public API
This is a large-scale refactoring across the codebase that replaces the custom
`gperr.Error` type with Go's standard `error` interface. The changes include:
- Replacing `gperr.Error` return types with `error` in function signatures
- Using `errors.New()` and `fmt.Errorf()` instead of `gperr.New()` and `gperr.Errorf()`
- Using `%w` format verb for error wrapping instead of `.With()` method
- Replacing `gperr.Subject()` calls with `gperr.PrependSubject()`
- Converting error logging from `gperr.Log*()` functions to zerolog's `.Err().Msg()` pattern
- Update NewLogger to handle multiline error message
- Updating `goutils` submodule to latest commit
This refactoring aligns with Go idioms and removes the dependency on
custom error handling abstractions in favor of standard library patterns.
- Correct BaseContext nil check in Context() method
- Move NewMonitor from monitor.go to new.go
- Export ErrDockerHealthCheckFailedTooManyTimes and add ErrDockerHealthCheckNotAvailable
- Return ErrDockerHealthCheckNotAvailable when container has no health check configured
- Only log first docker health check failure and skip logging for ErrDockerHealthCheckNotAvailable
- Use mon.Context() instead of mon.task.Context() to avoid nil panic
