Show all password entries with matching service when username is not provided while searching

[SonuBardai]

When there's multiple passwords associated with a single service, it helps organize the passwords by also adding the username which the password is linked with. A show password command looks for the exact match of [service + username]. It would be convenient if it had a broader scope where it first searched for matching services, and then go deeper into searching for specific username only if a username is provided. If there's no username provided in the search query then all password entries matching the service would make sense.

Current behavior

$ lockbox list
Service: instagram, Username: myaccount, Password: jOSjoewmgnosjgo
Service: facebook, Username: someusername-1, Password: OybNRFgdx7l5PK8f
Service: facebook, Username: someusername-2, Password: UJRJI1d2t2IqbEkq

$ lockbox show --service facebook --username someusername-1
Password: OybNRFgdx7l5PK8f

$ lockbox show --service facebook
Password not found

Desired behavior:

$ lockbox show --service facebook --username someusername-1
Password: OybNRFgdx7l5PK8f

$ lockbox show --service facebook
Username: someusername-1, Password: OybNRFgdx7l5PK8f
Username: someusername-2, Password: UJRJI1d2t2IqbEkq

$ lockbox show --service facebook --username someusername-1
Password: OybNRFgdx7l5PK8f

$ lockbox show --service facebook --username someusername-3
Password not found