docs: Fix BPNL Group Validation documentation for a valid Policy with a Collection

[bmg13]

Describe the bug

ℹ️ This issue is a result of the feedback obtained described in #1674 (comment).

According to the documentation, for creating a Policy with a constraint to match if the groups a BPNL is assigned are allowed to fetch the respective catalog, the rightOperand should be something similar to ["some-group-1", "some-group-2"], however that use is not working as expected, since the expanded value is the one being use for comparison instead of "simplified" values.

On the other hand, a comma-separated collection (in a single string) works properly, so the documentation should be updated to reflect that.

Context Information

For more context, please consult this issue.

Possible Implementation

In the documentation for BPN Group Validation, replace the ["some-group-1", "some-group-2"] in right operands to "some-group-1,some-group-2".