Validate metadata

[stellaprins]

Description

What is this PR

• Bug fix
• Addition of a new feature
• Other

Why is this PR needed?
_rich_atlas_metadata expects that the metadata has only a single comma, in a specific place. However, some atlasses have citation metadata without comma or containing multiple commas, for these there will be an error when trying to print their information to the screen. See #525 for more context.

What does this PR do?

• _rich_atlas_metadata does not split citation string up in two parts (using a comma as seperator) like before.
• validate_metadata function added to validate the type of metadata of generated atlasses

References

#525

How has this PR been tested?

• test_validate_metadata checks whether metadata is validated correctly for a few testcases
• Visual inspection of the rich panel before and after change (see screenshot below).

Before (left) and after (right; note the comma after "Wang et al 2020"):

Is this a breaking change?

No.

Does this PR require an update to the documentation?

No.

Checklist:

• The code has been tested locally
• Tests have been added to cover all new functionality (unit & integration)
• The documentation has been updated to reflect any changes
• The code has been formatted with pre-commit