Create CircleCI Orbs to notify slack to extend a lifetime of a GCP instance

[zoetrope]

What

The step to notify slack is used in multiple repositories.

• neco/.circleci/config.yml

  Line 62 in f179c65

  - run:

• https://github.com/cybozu-go/neco-apps/blob/49adaf249896d17049297d023092bf191c83ec20/.circleci/config.yml#L79

This step is the same in those repositories, so it should be shared using CircleCI Orbs.

Also, in the step, I want to send a mention to the corresponding user if possible.

How

Describe how to address the issue.

Checklist

• Finish implementation of the issue
• Test all functions
• Have enough logs to trace activities
• Notify developers of necessary actions