Added ApplicationInsightsPropertyFormatter for flattening complex properties

[olegKoshmeliuk]

Implemented new behavior for AI custom properties for better integration with Analytics queries
Fix for #13

Example:

logger.Information("Got request:{@string} and {@dto} ", "[\"string\"]",
                new
                {
                    number = 1,
                    list = new object[] {1, "test"},
                    inner = new {a = "a", b = "b"},
                });
//Will produce 

Old behavior:

{
  "LogLevel": "Information",
  "RenderedMessage": "Got request:\"[\\\"string\\\"]\" and { number: 1, list: [1, \"test\"], inner: { a: \"a\", b: \"b\" } }",
  "string": "\"[\\\"string\\\"]\"",
  "dto": "{ number: 1, list: [1, \"test\"], inner: { a: \"a\", b: \"b\" } }"
}

New behavior:

{
  "LogLevel": "Information",
  "MessageTemplate": "Got request:{@string} and {@dto}",
  "RenderedMessage": "Got request:\"[\\\"string\\\"]\" and { number: 1, list: [1, \"test\"], inner: { a: \"a\", b: \"b\" } }",
  "string": "[\"string\"]",
  "dto.number": "1",
  "dto.list.0": "1",
  "dto.list.1": "test",
  "dto.list.Count": "2",
  "dto.inner.a": "a",
  "dto.inner.b": "b"
}

[joergbattermann]

LGTM 👍 Thanks a lot @olegKoshmeliuk !!