Create endpoint to getParticipants for participants page

[davidscavnicky]

Create an endpoint that returns a list of participants, where each participant contains:

• email
• firstName
• lastName
• isRegistered
• invitedOn
• participantId (anonymous links)

/{{StudyID}} - queries should be made by a particular study

As for now, frontend needs to call 2 endpoints and merge the responses to get all data. This doesn’t allow the feature of sorting by invitedOn

[davidscavnicky]

this should be active, @jakdan99 added that there should be id as well in case the participant is anonymous. (The one that is generated by keycloak when the anonymous accounts are generated).

@xelahalo is okey to provide with participant id in case if its anonymous?

[davidscavnicky]

two cases: anonymous participants or participants in a study

1. what's the logic of showing accountId in anonymous studies?
   ( I mean if we do same implementation as for GET_PARTICIPANTS_ACCOUNT ).

2. isRegisteredOn takes from UserRepresentation "isVerified"; will return boolean for non-anonymous studies and NULL value for anonymous?, because it probably doesn't have a logic to check registration of generated users while doing an anonymous study user generation. @jakdan99 what do you think?

I don't know if it should be more thought through on the design or this is enough.