[RHCLOUD-39048] fix the error message for invalid 'type' and 'principal_type' query param value

[petracihalova]

Link(s) to Jira

• RHCLOUD-39048

Description of Intent of Change(s)

if you send request to list principals with invalid type value, the response contains Principal.Types.SERVICE_ACCOUNT for service-account value and similar for user value

{
    "errors": [
        {
            "detail": "type query parameter value 'foo' is invalid. [Principal.Types.SERVICE_ACCOUNT, Principal.Types.USER, 'all'] are valid inputs.",
            "source": "detail",
            "status": "400"
        }
    ]
}

this PR adds logic to convert values into strings

{
    "errors": [
        {
            "detail": "type query parameter value 'foo' is invalid. ['service-account', 'user', 'all'] are valid inputs.",
            "source": "detail",
            "status": "400"
        }
    ]
}

Local Testing

send request GET /principals/?type=foo
send request GET /groups/<uuid>/principals/?principal_type=foo

[petracihalova]

I added DO NOT MERGE label because we need to merge #1558 first and this PR has potential to create merge conflicts

[vbelchio]

QE: Passed (manual)