fix(crontab): Fixed that when sending SIGINT signal, it could not be stopped properly

[flc1125]

…e stopped properly

[what-the-diff]

PR Summary

• Updated .gitignore
  The .gitignore file, responsible for omitting certain files from tracking, now includes _example, ensuring that this file isn't unnecessarily considered in tracking updates.

• Documentation Update in crontab/README.md
  The documentation was updated in several aspects. First, references to the fmt package were replaced with the log package, offering more appropriate messaging utilities for running programs. Second, the creation of a NewCrontabServer function has been wrapped into the kratos.New function for a more streamlined setup process. Lastly, app.Run() was added to clarify that this function needs to be called to start the applicaction.

• Updated run function in crontab/server.go
  Changed the run function to return an error instead of void (nothing). Now, if any problem arises during the execution of this function, the error will be returned and can be handled appropriately.

• Improved Exception Handling
  Added a return ctx.Err() inside the run function in crontab/server.go, enhancing how we handle the errors in this function.

• Enhanced Logging in Stop Function
  Added s.log("crontab: server stopping") in the Stop function of crontab/server.go. This new log message helps identify when the server is stopping, improving the visibility of the server's lifecycle.