[ENHANCEMENT] Support maintenance windows

[tpoindessous]

Hi !

First, thanks for your work, we are using your provider quite often.

We would like to use it to handle maintenance windows : https://docs.pingdom.com/api/#tag/Maintenance/paths/~1maintenance~1{id}/put

Could you, please, tell us what is your current roadmap for this provider or if you think that you will not work on this subject ? Maybe we can provide a first work in a PR.

Thanks !

cc: @nlamirault

[tpoindessous]

This seems to be handled by this PR #98

Thanks !