Default unique_tags object precludes tagless model

[esherman-credo]

Expected Behavior

If model is untagged and evidence requirement specifies no tags, model should satisfy requirements.

Actual Behavior

Governance._unique_tags is an empty list by default. When a model with no tags is checked against requirements, the fact that there is no empty dictionary in the empty list causes the requirement to be marked as non-matching.
Unique tags default set here: https://github.com/credo-ai/credoai_connect/blob/develop/connect/governance/governance.py#L74

Comparison on this line https://github.com/credo-ai/credoai_lens/blob/develop/credoai/lens/lens.py#L456

Example output here:

Steps to Reproduce the Problem

1. Generate policy pack with no tags
2. Attempt to run Lens with model that has no tags

Solution Options

1. Change default unique_tags to be [{}] or similar
2. Here add an additional check to make sure one of model.tags or self.gov.unique_tags is non-empty. If both are empty, we shouldn't have an error.