Inconsistency in timestamps: some with, some without time zone

[SlowMo24]

Bug Description

The endpoint elements/count/groupBy/boundary returns timestamps with timezone

https://api.ohsome.org/v1/elements/count/groupBy/boundary?bboxes=8.67%2C49.39%2C8.71%2C49.42&filter=geometry%3Apoint%20and%20natural%3Dtree&time=2014-01-01

Response

{
  "attribution": {
    "url": "https://ohsome.org/copyrights",
    "text": "© OpenStreetMap contributors"
  },
  "apiVersion": "1.10.1",
  "groupByResult": [
    {
      "groupByObject": "boundary1",
      "result": [
        {
          "timestamp": "2014-01-01T00:00:00Z",
          "value": 850
        }
      ]
    }
  ]
}

while the endpoint elements/count/ratio/groupBy/boundary returns timestamps without timezone

https://api.ohsome.org/v1/elements/count/ratio/groupBy/boundary?bboxes=8.67%2C49.39%2C8.71%2C49.42&filter=geometry%3Apoint%20and%20natural%3Dtree&filter2=geometry%3Apoint%20and%20shop%3Dbakery&format=json&time=2014-01-01

Response

{
  "attribution": {
    "url": "https://ohsome.org/copyrights",
    "text": "© OpenStreetMap contributors"
  },
  "apiVersion": "1.10.1",
  "groupByBoundaryResult": [
    {
      "groupByObject": "boundary1",
      "ratioResult": [
        {
          "timestamp": "2014-01-01T00:00:00",
          "value": 850,
          "value2": 28,
          "ratio": 0.032941
        }
      ]
    }
  ]
}

General Information

• Version of the ohsome API: 1.10.1
• API instance https://api.ohsome.org/v1
• Affected endpoint: I have only teste elements/count/ratio/groupBy/boundary
• URL of your request (and request body if applicable): see above
• Used HTTP method: GET but it should not matter
• Utilized tool/library for the request: swagger or curl, should not matter

Expected Behaviour

Either always return a time zone, or never (which I would prefer).

Further Information

Error Messages, Logs, Screenshots

None

Additional Information

None

Notes

None

//cc @rp280

[tyrasd]

At first glance, it seems that the /elements/(aggregation)/ratio/groupBy/boundary is the only endpoint which does not return a timestamp with explicit Z timezone. The documentation has also always included the timezone in the examples. I agree that we should consistently always return the same format, but to limit the scope of the fix, let's stick to the format including the Z.