Policy endpoints should ignore masking strategy when the action is `access`

[mfbrown]

When the action of a policy is access and I attempt to update the policy via the Fides API, when I include a masking_strategy section, but not a configuration object within masking_strategy the API errors.

It would be easier to use the API to update policies if the endpoint ignored masking_strategy when action: access, since access requests don't require a masking strategy.