Update queries to support having multiple key-value pairs per index

[DRK3]

Update our query implementation to work in the way described here: https://github.com/decentralized-identity/secure-data-store/issues/34#issuecomment-700108603

Some specifics:

• Need to support having multiple key-value attribute pairs per index
• Need to make the equals object act as a filter as described in the post.

[DRK3]

Update: The query syntax is described here: https://identity.foundation/edv-spec/#searching-encrypted-documents