sda-cli reports maintenance window

[MalinAhlberg]

Please describe the feature
As a user, I want sda-cli to be able to tell me if maintenance is on-going, so that I know when to not start uploads etc.

Acceptance criteria

• sda-cli prints a warning if maintenance is on-going or soon starting?
• Tests verifying the changes are added

Additional context
This is a suggestion made in the Confluence Maintenance page.

Estimation of size: small/medium/big

Estimation of priority: low/medium/high