Implement method to run when a maintenance starts or ends

[ajoaoff]

Original issue opened by @ajoaoff at https://github.com/kytos/maintenance/issues/6.

Methods below need to be implemented.

https://github.com/kytos/maintenance/blob/50c63f27dce8b6f8d3d4a7b4fb080c582842b045/models.py#L141-L147

[viniarck]

This one is no longer needed based on how maintenance interruption events have evolved on 2023.1