fix: remove string TTL from workspace error responses (#3257)

- Rewrites some error messages to better integrate with the frontend (ttl_ms -> time until shutdown)
- Makes codersdk.ValidationError implement the error interface
- Only return validations if the error was a validation error, return detail otherwise (e.g. database error)

codersdk/error.go

@@ -1,6 +1,7 @@
 package codersdk
 
 import (
+	"fmt"
 	"net"
 
 	"golang.org/x/xerrors"
@@ -32,6 +33,12 @@ type ValidationError struct {
 	Detail string `json:"detail" validate:"required"`
 }
 
+func (e ValidationError) Error() string {
+	return fmt.Sprintf("field: %s detail: %s", e.Field, e.Detail)
+}
+
+var _ error = (*ValidationError)(nil)
+
 // IsConnectionErr is a convenience function for checking if the source of an
 // error is due to a 'connection refused', 'no such host', etc.
 func IsConnectionErr(err error) bool {