sda-auth can report if maintenance is on-going

[MalinAhlberg]

Please describe the feature
As a user, I want sda-auth to be able to report if maintencance is ongoing so that I can plan my work.

Acceptance criteria

• a parameter is added that checks if maintenance is on-going (or a list of planned dates)
• Tests verifying the changes are added

Additional context
This is a suggestion made in the Confluence Maintenance page.
The idea is that sda-cli could check with sda-auth if maintenance is on-going and report that to the user.
Related to NBISweden/sda-cli#436

Estimation of size: small/medium/big

Estimation of priority: low/medium/high