Add support batch requests

[khyurri]

Often you have to monitor many events at the same time. This puts a strain on the network, slow clients are even slower.

It is necessary to make batch requests.

For example:

POST /event/ with body will create only one event:

{
    "metricName": metricName,
    "durationMs": duration,
    "project": project
}

If client sends list of events, server can store they all:

[
{
    "metricName": metricName1,
    "durationMs": duration1,
    "project": project1
},
{
    "metricName": metricName2,
    "durationMs": duration2,
    "project": project2
},
...
]